[r=jtv][bug=1055935][author=rvb] Make the celery worker listen to the 'master' queue in addition to the default 'celery' queue.
This is a temporary workaround to cope with the fact that task routing is already in place and that the cluster tasks are routed to nodegroup.uuid already. Fortunately, right now, nodegroup.uuid = 'master' for the only existing nodegroup.