This patchset implements key rotation for the ceph-fs charm by
receiving the new pending key from the ceph-mon charm and
manually rotating it via Ceph's authtool. It makes use of the
'ceph-mds-relation-changed' hook for this.
Change-Id: I773f389f56d78cd7ce58f9f2b5e7d7695164acb1
func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/1202