Merge branch 'sh-add-ee-load-balancer-silencer' into 'master'

Add a Rails backtrace silencer for EE load balancing code

See merge request gitlab-org/gitlab!23667

config/initializers/backtrace_silencers.rb

 Rails.backtrace_cleaner.remove_silencers!
+
+# This allows us to see the proper caller of SQL calls in {development,test}.log
+if (Rails.env.development? || Rails.env.test?) && Gitlab.ee?
+  Rails.backtrace_cleaner.add_silencer { |line| line =~ %r(^ee/lib/gitlab/database/load_balancing) }
+end
+
 Rails.backtrace_cleaner.add_silencer { |line| line !~ Gitlab::APP_DIRS_PATTERN }