Fix nil user handling in UpdateMirrorService

Previously an exception was hit quite frequently:

```
NoMethodError: undefined method `can?' for nil:NilClass
  app/services/projects/update_mirror_service.rb:9:in `execute'
    unless current_user.can?(:push_code_to_protected_branches, project)
  lib/gitlab/metrics/instrumentation.rb:153:in `execute'
    retval   = super
  app/workers/repository_update_mirror_worker.rb:13:in `perform'
    result = Projects::UpdateMirrorService.new(@project, @current_user).execute
  lib/gitlab/sidekiq_middleware/memory_killer.rb:17:in `call'
    yield
  lib/gitlab/sidekiq_middleware/arguments_logger.rb:6:in `call'
    yield
...
(26 additional frame(s) were not displayed)
```

Closes #605

See merge request !434

Remote Mirrors should be disabled by default

REF: #548 

See merge request !428

Closes #605

[ci skip]

ES: Protecting notes for confidential issue in search result page

https://gitlab.com/gitlab-org/gitlab-ee/issues/575

If it goes to the patch release, please include following to the release blog post:
--------------------------------------------------
If you use Elasticsearch please run following command after upgrade:

```
# Omnibus installations
sudo gitlab-rake gitlab:elastic:reindex_model MODEL=Note

# Installations from source
bundle exec rake gitlab:elastic:reindex_model MODEL=Note RAILS_ENV=production
```
----------------------------------------------------

See merge request !500

Gracefully handle malformed DNs in LDAP group sync

Customer reported an emergency because group sync was blowing up with 'Badly formed DN'. It turns out their LDAP system inserts a blank member entry at the beginning of each LDAP group. When we try to parse this DN, group sync explodes. Obviously we should handle this error gracefully. This merge request catches the error, logs it, and moves on (skipping that entry).

See merge request !392

Bugfix: Remote config URL was not updated when mirror credentials were updated

The `after_save` callback was looking for changes only in the URL
without credentials, this was happening because we store the credentials
in a separate field.

REF: #547 

See merge request !426

Fix fast-forward merge requests git hooks validations

Current implementations checks git hooks during merge request action issued by Web UI to prevent a git merge action failing and not reporting back to the UI (introduced by !326).
The problem is that we shouldn't make the check the merge commit when we are using a Fast Forward merge type.

Fixes gitlab-org/gitlab-ee#598

See merge request !427

The `after_save` callback was looking for changes only in the URL without credentials,
this was happening because we store the credentials in a separate field.

Make it clear the license overusage is visible only to admins

Also make the text describing the number of licensed users consistent.

Closes #607, #610 

Screenshot:

![image](/uploads/61be740a35a4d4c778233645934554b6/image.png)


See merge request !423

Add some debug info for error related to fetching tags.

This will help us to debug: https://sentry.gitlap.com/gitlab/gitlabcom/issues/4469/events

See merge request !419

Closes #610

Closes #607

Add link to Upload License page in broadcast alert message.

That way admins can have a quick link at hand to upload the license.

See merge request !418

Minor updates after release



See merge request !424

Reduce load on DB for license upgrade check

1. Only check if the user is an admin
2. Cache the active user count for an hour

Helps gitlab-com/operations#298

See merge request !421

Add standard web hook headers to Jenkins CI post

Closes #534

The Jenkins web hook was not sending the standard web hook headers.
Specifically, the `gitlab-plugin` for Jenkins needs to use the
`X-GitLab-Event` header. This makes our EE service unable to work with
the newer GitLab Plugin for Jenkins.

See https://github.com/jenkinsci/gitlab-plugin/issues/272

See merge request !374

[ci skip]

1. Only check if the user is an admin
2. Cache the active user count for an hour

Helps gitlab-com/operations#298

Added back total weight on milestone view

![Screen_Shot_2016-05-25_at_13.31.56](/uploads/8530d92c05b97f719b6e42377ffe7b24/Screen_Shot_2016-05-25_at_13.31.56.png)

Should this go into a patch release?

Closes #501

See merge request !420

Closes #501

Fix repository mirror updates for new imports stuck in started

We were calling `RepositoryUpdateMirrorWorker` that sets the import status to `finished` and then add the import job. Then `update_mirror` didn't do anything but set the `import_status` to started. This should be now getting called in the right order... 

Closes https://gitlab.com/gitlab-com/operations/issues/287 and https://gitlab.com/gitlab-org/gitlab-ce/issues/17747

See merge request !416

This will help us to debug: https://sentry.gitlap.com/gitlab/gitlabcom/issues/4469/events

That way admins can have a quick link at hand to upload the license.

CE upstream



See merge request !415

Search through the filenames



See merge request !409

Add one more ES note to 8.8 update guide



See merge request !406