ceph/rbd_mirror: Optionally require presence of images in wait-helper

When you tell Ceph to resync mirrored RBD images it will in
practice remove and re-create the image.

At present the image state wait helper will happilly accept no
images in a pool as a positive outcome.

Add optional ``require_images_in`` parameter that allows the wait
helper to block even when no images are available in the pool (yet)

zaza/charm_tests/ceph/rbd_mirror/tests.py

@@ -68,7 +68,8 @@ class CephRBDMirrorBase(test_utils.OpenStackBaseTest):
 
     def wait_for_mirror_state(self, state, application_name=None,
                               model_name=None,
-                              check_entries_behind_master=False):
+                              check_entries_behind_master=False,
+                              require_images_in=[]):
         """Wait until all images reach requested state.
 
         This function runs the ``status`` action and examines the data it
@@ -85,6 +86,8 @@ class CephRBDMirrorBase(test_utils.OpenStackBaseTest):
                                             when used with state
                                             ``up+replying``.
         :type check_entries_behind_master: bool
+        :param require_images_in: List of pools to require images in
+        :type require_images_in: list of str
         :returns: True on success, never returns on failure
         """
         rep = re.compile(r'.*entries_behind_master=(\d+)')
@@ -92,7 +95,10 @@ class CephRBDMirrorBase(test_utils.OpenStackBaseTest):
             pool_status = self.run_status_action(
                 application_name=application_name, model_name=model_name)
             for pool, status in pool_status.items():
-                for image in status.get('images', []):
+                images = status.get('images', [])
+                if not len(images) and pool in require_images_in:
+                    break
+                for image in images:
                     if image['state'] and image['state'] != state:
                         break
                     if check_entries_behind_master:
@@ -304,7 +310,8 @@ class CephRBDMirrorControlledFailoverTest(CephRBDMirrorBase):
         self.wait_for_mirror_state(
             'up+replaying',
             application_name=self.application_name + self.site_b_app_suffix,
-            model_name=self.site_b_model)
+            model_name=self.site_b_model,
+            require_images_in['cinder-ceph', 'glance'])
 
 
 class CephRBDMirrorDisasterFailoverTest(CephRBDMirrorBase):