Multi delete of RBDs does not work properly

2017-02-21 14:25:52,931 - INFO - taskqueue.models#transition - Task Transition: Not Started -> Running
2017-02-21 14:25:52,933 - INFO - taskqueue.models#run_once - Running 1088: ceph.tasks.get_rbd_performance_data with [u'cc71083d-9221-4013-a1ec-775b19d88b6d', u'rbd', u'testRBD2'], {}. Estimated: None
2017-02-21 14:25:52,978 - INFO - taskqueue.models#finish_task - Task finished: ({u'used_size': 0, u'name': u'testRBD2', u'provisioned_size': 2147483648}, 43.9)
2017-02-21 14:25:52,979 - INFO - taskqueue.models#transition - Task Transition: Running -> Finished
2017-02-21 14:25:57,929 - INFO - taskqueue.models#transition - Task Transition: Not Started -> Running
2017-02-21 14:25:57,932 - INFO - taskqueue.models#run_once - Running 1089: ceph.tasks.get_rbd_performance_data with [u'cc71083d-9221-4013-a1ec-775b19d88b6d', u'rbd', u'testRBD1'], {}. Estimated: None
2017-02-21 14:25:58,211 - INFO - taskqueue.models#finish_task - Task finished: ({u'used_size': 0, u'name': u'testRBD1', u'provisioned_size': 2147483648}, 277.68)
2017-02-21 14:25:58,211 - INFO - taskqueue.models#transition - Task Transition: Running -> Finished
2017-02-21 14:25:59,360 - INFO - openattic_systemd#loggedfunc - Calling /ceph::remove_nagios_configs(dbus.Array([dbus.String(u'rbd')], signature=dbus.Signature('s')))
2017-02-21 14:25:59,361 - INFO - openattic_systemd#loggedfunc - Calling /ceph::write_rbd_nagios_configs()
2017-02-21 14:25:59,645 - ERROR - exception#custom_handler - Internal Server Error: None
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/rest_framework/views.py", line 400, in dispatch
    response = handler(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/rest_framework/mixins.py", line 194, in destroy
    obj.delete()
  File "/srv/openattic/backend/ceph/models.py", line 887, in delete
    self._update_nagios_configs()
  File "/srv/openattic/backend/ceph/models.py", line 895, in _update_nagios_configs
    ceph.write_rbd_nagios_configs()
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
DBusException: org.freedesktop.DBus.Python.rbd.ImageNotFound: Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/srv/openattic/backend/systemd/plugins.py", line 51, in loggedfunc
    return func(*args, **kwargs)
  File "/srv/openattic/backend/systemd/plugins.py", line 99, in wrapper
    return meth(self, *args, **kwargs)
  File "/srv/openattic/backend/ceph/systemapi.py", line 238, in write_rbd_nagios_configs
    for rbd in CephRbd.objects.filter(pool__name=pool.name):
  File "/srv/openattic/backend/nodb/models.py", line 164, in next
    if self._current > self._max:
  File "/srv/openattic/backend/nodb/models.py", line 175, in __getattribute__
    own_attr = super(NodbQuerySet, self).__getattribute__(attr_name)
  File "/usr/lib/python2.7/dist-packages/django/utils/functional.py", line 49, in __get__
    res = instance.__dict__[self.func.__name__] = self.func(instance)
  File "/srv/openattic/backend/nodb/models.py", line 86, in _max
    return len(self._filtered_data) - 1
  File "/srv/openattic/backend/nodb/models.py", line 175, in __getattribute__
    own_attr = super(NodbQuerySet, self).__getattribute__(attr_name)
  File "/usr/lib/python2.7/dist-packages/django/utils/functional.py", line 49, in __get__
    res = instance.__dict__[self.func.__name__] = self.func(instance)
  File "/srv/openattic/backend/nodb/models.py", line 145, in _filtered_data
    filtered = [obj for obj in self._data()
  File "/srv/openattic/backend/nodb/models.py", line 90, in _data
    objects = self.model.get_all_objects(context, query=self._query)
  File "/srv/openattic/backend/ceph/models.py", line 807, in get_all_objects
    rbd, pool=pool, id=CephRbd.make_key(pool, rbd['name'])))) for (rbd, pool) in rbds]
  File "/srv/openattic/backend/ceph/models.py", line 803, in <genexpr>
    for (image_name, pool)
  File "/srv/openattic/backend/ceph/librados.py", line 916, in image_old_format
    return self._call_librados(_action)
  File "/srv/openattic/backend/ceph/librados.py", line 919, in _call_librados
    return call_librados(self.fsid, func, timeout)
  File "/srv/openattic/backend/ceph/librados.py", line 266, in call_librados
    raise res
ImageNotFound: error opening image testRBD1 at snapshot None