Merge branch 'ash.mckenzie/fix-rails-sidekiq-rails-module-namespacing' into 'master'

Ensure when accessing Rails, we really get ::Rails (and not Sidekiq::Rails)

See merge request gitlab-org/gitlab-ce!18730

config/initializers/forbid_sidekiq_in_transactions.rb

@@ -27,7 +27,7 @@ module Sidekiq
                 Use an `after_commit` hook, or include `AfterCommitQueue` and use a `run_after_commit` block instead.
                 MSG
               rescue Sidekiq::Worker::EnqueueFromTransactionError => e
-                Rails.logger.error(e.message) if Rails.env.production?
+                ::Rails.logger.error(e.message) if ::Rails.env.production?
                 Gitlab::Sentry.track_exception(e)
               end
             end