Mimic clients can't talk to mixed M+N Cluster

[Chris MacNaughton]

When trying to upgrade from Mimic to Nautilus, the clients on the Mimic nodes fail to talk to the monitor cluster as soon as the first unit is upgraded:

# ceph -s
Traceback (most recent call last):
  File "/usr/bin/ceph", line 1241, in <module>
    retval = main()
  File "/usr/bin/ceph", line 1165, in main
    sigdict = parse_json_funcsigs(outbuf.decode('utf-8'), 'cli')
  File "/usr/lib/python3/dist-packages/ceph_argparse.py", line 788, in parse_json_funcsigs
    cmd['sig'] = parse_funcsig(cmd['sig'])
  File "/usr/lib/python3/dist-packages/ceph_argparse.py", line 728, in parse_funcsig
    raise JsonFormat(s)
ceph_argparse.JsonFormat: unknown type CephBool

The monitor cluster is actually still functional according to that same command on the newly Nautilus unit:

$ sudo ceph -s
  cluster:
    id: 2734983c-c88f-11e9-b6f9-fa163e8108c2
    health: HEALTH_OK

  services:
    mon: 3 daemons, quorum juju-a792f2-ceph-mimic-upgrade-0,juju-a792f2-ceph-mimic-upgrade-1,juju-a792f2-ceph-mimic-upgrade-2 (age 3m)
    mgr: juju-a792f2-ceph-mimic-upgrade-0(active), standbys: juju-a792f2-ceph-mimic-upgrade-1, juju-a792f2-ceph-mimic-upgrade-2
    osd: 3 osds: 3 up, 3 in
    rgw: 1 daemon active (juju-a792f2-ceph-mimic-upgrade-6)

  data:
    pools: 15 pools, 46 pgs
    objects: 187 objects, 1.1 KiB
    usage: 3.0 GiB used, 27 GiB / 30 GiB avail
    pgs: 46 active+clean

[Chris MacNaughton (chris.macnaughton)]

Configuring the `ceph` command to run on an upgraded monitor unit only (`ceph -m $MON_IP`) causes the command to work successfully

[Edward Hope-Morley (hopem)]

See fix in https://bugs.launchpad.net/charm-ceph-mon/+bug/1897594