[Rails5] Fix Arel::UpdateManager calls

In Rails 5.0 `Arel::UpdateManager.new` doesn't expect any parameters.

This commit makes the migration not pass any parameters if on Rails 5.0.

db/migrate/20161207231620_fixup_environment_name_uniqueness.rb

 class FixupEnvironmentNameUniqueness < ActiveRecord::Migration
+  include Gitlab::Database::ArelMethods
   include Gitlab::Database::MigrationHelpers
 
   DOWNTIME = true
@@ -41,7 +42,7 @@ class FixupEnvironmentNameUniqueness < ActiveRecord::Migration
 
     conflicts.each do |id, name|
       update_sql =
-        Arel::UpdateManager.new(ActiveRecord::Base)
+        arel_update_manager
           .table(environments)
           .set(environments[:name] => name + "-" + id.to_s)
           .where(environments[:id].eq(id))

db/migrate/20161207231626_add_environment_slug.rb

@@ -2,6 +2,7 @@
 # for more information on how to write migrations for GitLab.
 
 class AddEnvironmentSlug < ActiveRecord::Migration
+  include Gitlab::Database::ArelMethods
   include Gitlab::Database::MigrationHelpers
 
   DOWNTIME = true
@@ -19,7 +20,7 @@ class AddEnvironmentSlug < ActiveRecord::Migration
     finder = environments.project(:id, :name)
 
     connection.exec_query(finder.to_sql).rows.each do |id, name|
-      updater = Arel::UpdateManager.new(ActiveRecord::Base)
+      updater = arel_update_manager
         .table(environments)
         .set(environments[:slug] => generate_slug(name))
         .where(environments[:id].eq(id))

db/post_migrate/20161109150329_fix_project_records_with_invalid_visibility.rb

 class FixProjectRecordsWithInvalidVisibility < ActiveRecord::Migration
+  include Gitlab::Database::ArelMethods
   include Gitlab::Database::MigrationHelpers
 
   BATCH_SIZE = 500
@@ -33,7 +34,7 @@ class FixProjectRecordsWithInvalidVisibility < ActiveRecord::Migration
       end
 
       updates.each do |visibility_level, project_ids|
-        updater = Arel::UpdateManager.new(ActiveRecord::Base)
+        updater = arel_update_manager
           .table(projects)
           .set(projects[:visibility_level] => visibility_level)
           .where(projects[:id].in(project_ids))

db/post_migrate/20170324160416_migrate_user_activities_to_users_last_activity_on.rb

 # rubocop:disable Migration/UpdateLargeTable
 class MigrateUserActivitiesToUsersLastActivityOn < ActiveRecord::Migration
+  include Gitlab::Database::ArelMethods
   include Gitlab::Database::MigrationHelpers
 
   disable_ddl_transaction!
@@ -39,7 +40,7 @@ class MigrateUserActivitiesToUsersLastActivityOn < ActiveRecord::Migration
     activities = activities(day.at_beginning_of_day, day.at_end_of_day, page: page)
 
     update_sql =
-      Arel::UpdateManager.new(ActiveRecord::Base)
+      arel_update_manager
         .table(users_table)
         .set(users_table[:last_activity_on] => day.to_date)
         .where(users_table[:username].in(activities.map(&:first)))