The "ceph mon_status" command seems to have disappeared on octopus and
later, and is replaced by "ceph quorum_status". This changes the
get_mon_map() function to detect the underlying ceph version and do the
right thing.
Note that the fix is actually in charm-helpers, and this has been
manually synced into the charm [1].
[1] https://github.com/juju/charm-helpers/pull/659
Change-Id: I59cf6fc19cf2a91b0aef37059cdb0ed37379b5cb
Closes-Bug: #1951094
9e5f668299