Enable multiple compatible Rubocop cops

## What does this MR do?

This MR enables multiple Rubocop cops, that are already compatible with
our codebase. See #17406.

Cops enabled:

```text
Style/ArrayJoin:
  Description: Use Array#join instead of Array#*.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#array-join
----------------
Style/Attr:
  Description: Checks for uses of Module#attr.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#attr
----------------
Style/BlockComments:
  Description: Do not use block comments.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-block-comments
----------------
Style/ClassMethods:
  Description: Use self when defining module/class methods.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#def-self-class-methods
----------------
Style/EndBlock:
  Description: Avoid the use of END blocks.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-END-blocks
----------------
Style/EvenOdd:
  Description: Favor the use of Fixnum#even? && Fixnum#odd?
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#predicate-methods
----------------
Style/FileName:
  Description: Use snake_case for source file names.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#snake-case-files
  ExpectMatchingDefinition: false
----------------
Style/FirstMethodParameterLineBreak:
  Description: Checks for a line break before the first parameter in a multi-line method
    parameter definition.
----------------
Style/FlipFlop:
  Description: Checks for flip flops
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-flip-flops
----------------
Style/GlobalVars:
  Description: Do not introduce global variables.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#instance-vars
  Reference: http://www.zenspider.com/Languages/Ruby/QuickRef.html
----------------
Style/IfWithSemicolon:
  Description: Do not use if x; .... Use the ternary operator instead.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-semicolon-ifs
----------------
Style/LambdaCall:
  Description: Use lambda.call(...) instead of lambda.(...).
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#proc-call
  EnforcedStyle: call
----------------
Style/MethodName:
  Description: Use the configured style when naming methods.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#snake-case-symbols-methods-vars
  EnforcedStyle: snake_case
----------------
Style/MultilineMethodDefinitionBraceLayout:
  Description: Checks that the closing brace in a method definition is symmetrical with
    respect to the opening brace and the method parameters.
----------------
Style/NestedModifier:
  Description: Avoid using nested modifiers.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-nested-modifiers
----------------
Style/OpMethod:
  Description: When defining binary operators, name the argument other.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#other-arg
----------------
Style/SignalException:
  Description: Checks for proper usage of fail and raise.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#prefer-raise-over-fail
  EnforcedStyle: only_raise
----------------
Style/SpaceAfterNot:
  Description: Tracks redundant space after the ! operator.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-space-bang
----------------
Style/SpaceBeforeSemicolon:
  Description: No spaces before semicolons.
----------------
Style/SpaceInsideRangeLiteral:
  Description: No spaces inside range literals.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#no-space-inside-range-literals
----------------
Style/SpaceInsideStringInterpolation:
  Description: Checks for padding/surrounding spaces inside string interpolation.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#string-interpolation
  EnforcedStyle: no_space
----------------
Style/StabbyLambdaParentheses:
  Description: Check for the usage of parentheses around stabby lambda arguments.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#stabby-lambda-with-args
  EnforcedStyle: require_parentheses
----------------
Style/StringMethods:
  Description: Checks if configured preferred methods are used over non-preferred.
  PreferredMethods:
    intern: to_sym
----------------
Style/VariableInterpolation:
  Description: Don't interpolate global, instance and class variables directly in strings.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#curlies-interpolate
----------------
Style/VariableName:
  Description: Use the configured style when naming variables.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#snake-case-symbols-methods-vars
  EnforcedStyle: snake_case
----------------
Style/WhenThen:
  Description: Use when x then ... for one-line cases.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#one-line-cases
----------------
Style/WhileUntilModifier:
  Description: Favor modifier while/until usage when you have a single-line body.
  StyleGuide: https://github.com/bbatsov/ruby-style-guide#while-as-a-modifier
  MaxLineLength: 80
```

Closes #17406 

See merge request !4286

Fixed issue with GitLab import buttons having a spinner

![import](/uploads/db635f1d62affefca027d5fd4f545cd1/import.gif)

Closes #17232

See merge request !4276

Add a gitlab:db:configure rake task to handle conditionally seeding or
migrating the database.

Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/17328

See merge request !4062

Move tags to column in generic_commit_status

Part of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4249    

cc @ayufan 



See merge request !4277

[ci skip]

Fix grammar and wording in text on various pages.

## What does this MR do?

Fixes various grammatical and/or wording issues I found while copyediting on the plane :)

## Why was this MR needed?

Incorrect grammar and weird/confusing wording makes the product look less polished and professional.

See merge request !4237

Increased zindex of layout nav

This fixes issues where group inputs would be above the dropdown in the nav

![Screen_Shot_2016-05-17_at_10.14.18](/uploads/08e4a43922051c28377ae6f34725ccc6/Screen_Shot_2016-05-17_at_10.14.18.png)

Closes #17524

See merge request !4176

Switch the gitlab:db:configure task to use tables.any? instead of looking specifically for the schema_migrations table

Enable RSpec/NotToNot cop and auto-correct offenses

Ref: https://gitlab.com/gitlab-org/gitlab-ce/issues/17761

See merge request !4267

Fixed issue with button color when no CI enabled

## What does this MR do?

Fixes an issue with the color of the merge button when no CI is setup.

## What are the relevant issue numbers?

Closes #17844

## Screenshots

![Screen_Shot_2016-05-25_at_09.58.44](/uploads/87aac74c5e2f8bfd2831e99c5915856d/Screen_Shot_2016-05-25_at_09.58.44.png)

See merge request !4287

Signed-off-by: Alfredo Sumaran <alfredo@gitlab.com>

Fix concurrent request when updating build log in browser

If you have a slow internet connection the trace will not be updated correctly. We need to check if our request is the latest one.

Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/17535

See merge request !4183

Closes #17844

Fix backups if registry is disabled

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17749

See merge request !4263

Changed the Slack build message to use the singular duration if necessary

## What does this MR do?

Previously, the Slack build notification would say "second(s)" even when the duration was only 1 second. This MR fixes that. This is my first time writing Ruby code and my first MR on Gitlab, so feedback is very much appreciated!

See merge request !4253

This fixes issues where group inputs would be above the dropdown in the nav

Closes #17524

Closes #17406

Update health_check.md - Fix spelling of admin/health_check path.  [ci skip]

## What does this MR do?
Fix the spelling of admin/heath_check to admin/health_check in health_check documentation

## Are there points in the code the reviewer needs to double check?
No

## Why was this MR needed?
Fix a spelling error that may mislead a user on the proper URL/Path to check the GitLab health.

## What are the relevant issue numbers?

## Screenshots (if relevant)

See merge request !4282

Updated snippets UI

![Screen_Shot_2016-05-18_at_14.11.54](/uploads/2544351e50f19a36c4ba9a7a92d5544b/Screen_Shot_2016-05-18_at_14.11.54.png)

Closes #14328

See merge request !4194

Project settings UI update

![Screen_Shot_2016-05-16_at_16.42.55](/uploads/2e308cbf26a002fc411c3e84b663a5d1/Screen_Shot_2016-05-16_at_16.42.55.png)![Screen_Shot_2016-05-16_at_16.43.01](/uploads/8d983c43307c65852efe002f6e9482d9/Screen_Shot_2016-05-16_at_16.43.01.png)![Screen_Shot_2016-05-16_at_16.43.16](/uploads/6124e0600cc0e5b309a60b065409d537/Screen_Shot_2016-05-16_at_16.43.16.png)![Screen_Shot_2016-05-16_at_16.43.13](/uploads/177976c2c08034e096e7ebdcad1f369f/Screen_Shot_2016-05-16_at_16.43.13.png)

See merge request !4162

Clicking changes tab scrolls the window to show the content

When you click on the changes tab in a merge request, it will now scroll the window down to the content.

![scroll](/uploads/c5db23e1c32b1fe62bf4efb815b3f055/scroll.gif)

Closes #15133

See merge request !4192