Allow a user to be an "Auditor"

An auditor user is intended to be user with read-only access to all projects and
groups. Access to the admin area and any project settings pages are disallowed

This commit lays the initial groundwork for this concept - adding an `auditor`
column to the `users` table, as well as a few supplements.

app/models/user.rb

@@ -123,6 +123,7 @@ class User < ActiveRecord::Base
   validate :unique_email, if: ->(user) { user.email_changed? }
   validate :owns_notification_email, if: ->(user) { user.notification_email_changed? }
   validate :owns_public_email, if: ->(user) { user.public_email_changed? }
+  validate :cannot_be_admin_and_auditor
   validates :avatar, file_size: { maximum: 200.kilobytes.to_i }
 
   before_validation :generate_password, on: :create
@@ -453,6 +454,12 @@ class User < ActiveRecord::Base
     end
   end
 
+  def cannot_be_admin_and_auditor
+    if admin? && auditor?
+      errors.add(:admin, "user cannot also be an Auditor.")
+    end
+  end
+
   # Returns the groups a user has access to
   def authorized_groups
     union = Gitlab::SQL::Union.

db/migrate/20170120123345_add_column_auditor_to_users.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddColumnAuditorToUsers < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    add_column_with_default :users, :auditor, :boolean, default: false, allow_null: false
+  end
+end

db/schema.rb

@@ -1452,6 +1452,7 @@ ActiveRecord::Schema.define(version: 20170204181513) do
     t.string "incoming_email_token"
     t.string "organization"
     t.boolean "authorized_projects_populated"
+    t.boolean "auditor", default: false, null: false
   end
 
   add_index "users", ["admin"], name: "index_users_on_admin", using: :btree

spec/factories/users.rb

@@ -14,6 +14,10 @@ FactoryGirl.define do
       admin true
     end
 
+    trait :auditor do
+      auditor true
+    end
+
     trait :external do
       external true
     end