Fix linting issue in testing framework

Add 503 as possible return code for Gnocchi. It's unavailable without
Ceph.

Change-Id: I3516374b875b6d89408a4fe05c8e73d6e29ba19d
Signed-off-by: Guillaume Boutry <guillaume.boutry@canonical.com>

ops-sunbeam/ops_sunbeam/test_utils.py

@@ -726,20 +726,22 @@ def get_harness(  # noqa: C901
             services: list[str],
             timeout: float = 30.0,
             delay: float = 0.1,
-        ) -> None:
+        ) -> ops.pebble.ChangeID:
             """Record start service events."""
-            super().start_services(services, timeout, delay)
+            change_id = super().start_services(services, timeout, delay)
             container_calls.add_start(self.container_name, services)  # type: ignore
+            return change_id
 
         def stop_services(
             self,
             services: List[str],
             timeout: float = 30.0,
             delay: float = 0.1,
-        ) -> None:
+        ) -> ops.pebble.ChangeID:
             """Record stop service events."""
-            super().stop_services(services, timeout, delay)
+            change_id = super().stop_services(services, timeout, delay)
             container_calls.add_stop(self.container_name, services)  # type: ignore
+            return change_id
 
     class _OSTestingModelBackend(_TestingModelBackend):
         def get_pebble(self, socket_path: str) -> _OSTestingPebbleClient:

tests/local/zaza/sunbeam/charm_tests/keystone/setup.py

@@ -24,7 +24,7 @@ from zaza.openstack.charm_tests.keystone.setup import (
 
 SERVICE_CODES = {
     # gnocchi is not started because no ceph relation
-    "gnocchi": [requests.codes.bad_gateway],
+    "gnocchi": [requests.codes.bad_gateway, requests.codes.service_unavailable],
     "heat-cfn": [requests.codes.bad_request],
     "heat": [requests.codes.bad_request],
 }