Log the find command used

lib/gitlab/background_migration/prepare_untracked_uploads.rb

@@ -82,6 +82,8 @@ module Gitlab
         cmd = %w[ionice -c Idle] + cmd if ionice_is_available?
+        Rails.logger.info "PrepareUntrackedUploads find command: \"#{cmd.join(' ')}\""
+
         cmd
       end