ceph-conf: do not log

If you are querying the conf for an osd and it has a log configured, we 
should not generate any log activity.

This isn't super pretty, but it is much less intrusive that wiring a 'do not
log' flag down into CephContext and a zillion other places.

Fixes: #7849 Signed-off-by: Sage Weil <sage@inktank.com>