Some RBD mirror tests are failing intermittently. The issue is actually in the ceph-mon charm, specifically the osd-relation entry point. The call to `notify_rbd_mirrors()` sometimes fail with the following traceback:
```
2022-07-15 15:10:06 INFO unit.ceph-mon-b/1.juju-log server.go:319 osd:27: mon cluster in quorum and osds bootstrapped - providing rbd-mirror client with keys
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 Traceback (most recent call last):
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/hooks/osd-relation-changed", line 1351, in <module>
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 hooks.execute(sys.argv)
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/hooks/charmhelpers/core/hookenv.py", line 962, in execute
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 self._hooks[hook_name]()
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/hooks/osd-relation-changed", line 886, in osd_relation
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 notify_rbd_mirrors()
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/hooks/osd-relation-changed", line 596, in notify_rbd_mirrors
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 rbd_mirror_relation(relid=relid, unit=unit, recurse=False)
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/hooks/osd-relation-changed", line 1019, in rbd_mirror_relation
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 'pools': json.dumps(ceph.list_pools_detail(), sort_keys=True),
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/lib/charms_ceph/utils.py", line 3112, in list_pools_detail
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 'quota': get_pool_quota(pool),
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/var/lib/juju/agents/unit-ceph-mon-b-1/charm/lib/charms_ceph/utils.py", line 3049, in get_pool_quota
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 output = subprocess.check_output(
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/usr/lib/python3.8/subprocess.py", line 415, in check_output
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 File "/usr/lib/python3.8/subprocess.py", line 516, in run
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 raise CalledProcessError(retcode, process.args,
2022-07-15 15:10:07 WARNING unit.ceph-mon-b/1.osd-relation-changed logger.go:60 subprocess.CalledProcessError: Command '['ceph', '--id', 'admin', 'osd', 'pool', 'get-quota', 'device_health_metrics']' returned non-zero exit status 2.
```
It appears to match other people's issues with device health metrics and the corresponding ceph module.
