An extra permission for rbd mirror on focal

Adding mon allow r for rbd mirror clients to fix failure to query
mirror pool status.

Change-Id: I63d9f137556b8aef379ee54ea977094722dbf032
Partial-Bug: #1879464

charms_ceph/utils.py

@@ -1139,7 +1139,7 @@ osd_upgrade_caps = collections.OrderedDict([
 ])
 
 rbd_mirror_caps = collections.OrderedDict([
-    ('mon', ['profile rbd']),
+    ('mon', ['profile rbd; allow r']),
     ('osd', ['profile rbd']),
     ('mgr', ['allow r']),
 ])

unit_tests/test_utils.py

@@ -973,7 +973,7 @@ class CephTestCase(unittest.TestCase):
         _get_named_key.assert_called_once_with(
             name='someid',
             caps=collections.OrderedDict([
-                ('mon', ['profile rbd']),
+                ('mon', ['profile rbd; allow r']),
                 ('osd', ['profile rbd']),
                 ('mgr', ['allow r']),
             ])