celery: queue utilities addition
celery: queue utilities addition

* Adds some utility functions for inspecting active Celery queue
  status and running tasks.

Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>
Signed-off-by: Jan Aage Lavik <8d55e006a1b29770f275a5c59a7341f17f8e69d5@cern.ch>

inveniosoftware/invenio-celery,tiborsimko/invenio-celery,tiborsimko/invenio-celery,inveniosoftware/invenio-celery