CSIT Sporadic failures - tempest.api.network precommit_delete failure on security group delete

File "tempest/test.py", line 190, in tearDownClass
 six.reraise(etype, value, trace)
 File "tempest/test.py", line 173, in tearDownClass
 teardown()
 File "tempest/test.py", line 477, in clear_credentials
 cls._creds_provider.clear_creds()
 File "tempest/lib/common/dynamic_creds.py", line 459, in clear_creds
 self._cleanup_default_secgroup(creds.tenant_id)
 File "tempest/lib/common/dynamic_creds.py", line 406, in _cleanup_default_secgroup
 nsg_client.delete_security_group(secgroup['id'])
 File "tempest/lib/services/network/security_groups_client.py", line 59, in delete_security_group
 return self.delete_resource(uri)
 File "tempest/lib/services/network/base.py", line 41, in delete_resource
 resp, body = self.delete(req_uri)
 File "tempest/lib/common/rest_client.py", line 301, in delete
 return self.request('DELETE', url, extra_headers, headers, body)
 File "tempest/lib/common/rest_client.py", line 659, in request
 self._error_checker(resp, resp_body)
 File "tempest/lib/common/rest_client.py", line 780, in _error_checker
 raise exceptions.Conflict(resp_body, resp=resp)
 tempest.lib.exceptions.Conflict: An object with that identifier already exists
 Details:
{u'message': u'Security Group 462df320-f024-4810-85a7-5b1195ee3602 cannot perform precommit_delete due to Callback networking_odl.common.callback.OdlSecurityGroupsHandler.sg_callback_precommit--9223372036854618144 failed with "argument of type \'NoneType\' is not iterable".', u'type': u'SecurityGroupInUse', u'detail': u''}