helper subroutine which finds out whether or not Gearman is enabled in the configuration
enqueue AddDefaultFeeds on Gearman right after adding new media
After adding new media, enqueue each unmoderated media_id one-by-one.
This achieves better atomicity, allows one to run multiple AddDefaultFeeds workers in parallel, and takes care of a race condition when new media is added when an instance of AddDefaultFeeds is already running.