mon: fix leak of MOSDFailure messages

We need to discard/cancel/free the failure report messages before we
cancel a report out.  Assert in the dtor to ensure we didn't forget.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: do not leak no_reply messages

I think I assumed no_reply() was releasing the references, but it is
not.  Which is better, since send_reply() doesn't either.  Fix the leaks
by dropping the message ref explicitly.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>