RBD: ceph.tasks.get_rbd_performance_data Tasks fails if RBD was deleted

017-04-06 19:32:35,278 - INFO - taskqueue.models#transition - Task Transition: Not Started -> Running
2017-04-06 19:32:35,281 - INFO - taskqueue.models#run_once - Running 14: ceph.tasks.get_rbd_performance_data with [u'xxx', u'test', u'rbd'], {}. Estimated: None
2017-04-06 19:32:35,325 - ERROR - taskqueue.models#run_once - Failed to run "ceph.tasks.get_rbd_performance_data with [u'xxx', u'test', u'rbd'], {}" created "2017-04-06 19:32:31.574484"
Traceback (most recent call last):
  File "/usr/share/openattic/taskqueue/models.py", line 79, in run_once
    res = task.run_once()
  File "/usr/share/openattic/taskqueue/models.py", line 239, in run_once
    res = self.wrapper.call_now(*self.args, **self.kwargs)
  File "/usr/share/openattic/taskqueue/models.py", line 316, in call_now
    return self._orig_func(*args, **kwargs)
  File "/usr/share/openattic/ceph/tasks.py", line 77, in get_rbd_performance_data
    disk_usage = api.image_disk_usage(pool_name, image_name)
  File "/usr/share/openattic/ceph/librados.py", line 779, in image_disk_usage
    '--pool', pool_name, '--image', name, '--format', 'json'])
  File "/usr/lib64/python2.7/subprocess.py", line 219, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
CalledProcessError: Command '['rbd', 'disk-usage', '--cluster', 'ceph', '--pool', u'test', '--image', u'rbd', '--format', 'json']' returned non-zero exit status 2
2017-04-06 19:32:35,329 - INFO - taskqueue.models#finish_task - Task finished: Command '['rbd', 'disk-usage', '--cluster', 'ceph', '--pool', u'test', '--image', u'rbd', '--format', 'json']' returned non-zero exit status 2
2017-04-06 19:32:35,329 - INFO - taskqueue.models#transition - Task Transition: Running -> Exception