The old name was very confusing, and this fits the convention of "the
processor for the signups" queue a la "process_user_activity".
This requires doing a
supervisorctl stop humbug-workers:humbug-events-subscribe-new-users
puppet apply
to deploy the supervisord configuration changes and properly restart
the signups queue.
(imported from commit 0ee2dad837142afa64025446e22956709771a192)
