ceph: do not print status to output file when talking to old mons

The old cli would send the status message to stdout instead of stderr;
we try to emulate that behavior when talking to old monitors because
they send some useful data to outs instead of the data payload.
However, when outputting to a *file*, the outs would still go to
stdout.  Maintain that so that, e.g.,

 ceph mon getmap -o /tmp/foo

doesn't prefix the monmap with 'got latest monmap\n'.

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