mon: make 'log ...' command wait for commit before reply

Previously we would just dump the command argument to our local log client
and reply immediately, which could lose the message if we then restarted.
Instead, commit directly and wait before replying.

Also, log as the actual client, not as the monitor processing the message.

Fixes: #5409
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Dan Mick <dan.mick@inktank.com>
mds: make 'mds compat rm_*compat' idempotent

Signed-off-by: Sage Weil <sage@inktank.com>
mon: drop deprecated 'stop_cluster'

Signed-off-by: Sage Weil <sage@inktank.com>
qa/workunits/cephtool/test.sh: fix and cleanup several tests

Signed-off-by: Sage Weil <sage@inktank.com>