mon/MonClient: finsih authenticate() only after we get monmap; fix 'tell mgr'

mon/MonClient: finsih authenticate() only after we get monmap; fix 'tell mgr'

We used to get a valid monmap before we finished the MAuth exchange and
returned from authenticate().  Now, we finish authenticating before we even
send or receive a message, so authenticate() returns quickly.  This
confuses many callers, and is probably a bad idea.  So, rejigger the
_finish_auth and _finish_hunting callers so that we finish hunting as soon
as we have picked a mon but don't finish_auth if we have not gotten our
first monmap.

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