mgr/DaemonServer: include details in 'osd ok-to-stop' output

mgr/DaemonServer: include details in 'osd ok-to-stop' output

Include specifics about which pgs are affect, which pgs prevent us from
being ok to stop, etc.

The primary downside I see here is that a success and failure output will
look more similar to a human user

Signed-off-by: Sage Weil <sage@newdream.net>
(cherry picked from commit 791952cc01201010f298033003ba52374cc0159f)