* Before, we had a special group, tower, that ran any async work that
tower needed done. This allowed users fine grain control over which
nodes did background work. However, this granularity was too complicated
for users. So now, all tower system work goes to a special non-user
exposed celery queue. Tower remains the fallback instance group to
execute jobs on. The tower group will be created upon install and
protected from deletion.
* Purging old task manager unit tests
* Migrating those tests to functional tests
* Updating fixtures and factories to support a change in the way the
task manager is tested
* Fix an issue with the mk_credential fixture when used in functional
tests. Previously it had trouble with multiplel invocations when
persistence was used
