After "ceph mgr module enable", new module's commands should be usable immediately
Currently, commands for a newly enabled module will appear missing until the mgr daemon has come back up after restart and reported itself to the monitors.
For example, this doesn't work (or is at least racy):
ceph mgr module enable status ceph fs status <-- this will give EINVAL because the mgr didn't restart just yet, it'll start working in a second.
We need something to happen on the mons so that the CLI knows to not EINVAL any commands until the newly-started mgr has reported the new module's commands.
This is not absolutely functionally necessary, but will make the life of anyone doing any scripting much simpler.