osd/mon/mds: unify usage text, always use stdout

osd/mon/mds: unify usage text, always use stdout

This unifies the first line of usage text: angle brackets
to indicate a mandatory option, and uppercase ID to match
the output from generic_server_usage().  It also ensures
ceph-mon prints all of its usage information to stdout,
same as the other daemons.

Signed-off-by: Tim Serong <tserong@suse.com>