[shutdown/reboot] Verify if one or more ceph-mon units can get shut down or rebooted

[Xav Paice]

* Command
juju verify reboot --units ceph-mon/0 [UNITS...]
juju verify shutdown --units ceph-mon/0 [ceph-mon/1 ...]

Expected behavior:
* "juju-verify" runs a “verify” action against ceph-mon
 - Check if HEALTH_OK (reuse code from the “get-health” action)
 - Check if removing this unit or units will mean that quorum is lost for ceph-mons, i.e. less than 50% remain online after the event.
 - if either check returns false, verification is considered failed.

Ceph actions required:
* ceph-mon: get-health (already exists)
 - Verify the cluster health
 - New ceph-mon units shutdowns need HEALTH_OK
* ceph-mon: get-quorum-status (new)
 - run `ceph quorum_status -f json` on the ceph-mon unit, save result as 'status'
 - return a list of known mon names, from status['monmap']['mons']
 - return a list of online mons, from status['quorum_names']

[Xav Paice (xavpaice)]

Added charm-ceph-mon to track the addition of a get-quorum-status action.

[Robert Gildein (rgildein)]

The section on checking the state of the Ceph cluster is part of a bug [1] for which MP already exists.

[1]: https://bugs.launchpad.net/juju-verify/+bug/1917596

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-ceph-mon/+/778837
Committed: https://opendev.org/openstack/charm-ceph-mon/commit/282e23416f75e8fc4c0fc81c7ef68cedf6afe426
Submitter: "Zuul (22348)"
Branch: master

commit 282e23416f75e8fc4c0fc81c7ef68cedf6afe426
Author: Xav Paice <email address hidden>
Date: Fri Mar 5 17:01:14 2021 +1300

    Add get-quorum-status action

    Adds a new get-quorum-status action to return some distilled info from
    'ceph quorum_status', primarily for verification of which mon units are
    online.

    Partial-Bug: #1917690

    Change-Id: I608832d849ee3e4f5d150082c328b63c6ab43de7