osd: trigger discover_all_missing after replay delay

osd: trigger discover_all_missing after replay delay

We were calling discover_all_missing only when we went immediately active,
not after we were in the replay state (which triggers from a timer event
that calls OSD::activate_pg().  Move the call into PG::activate() so that
we catch both callers.

This requires passing in a query_map from the caller.  While we're at it,
clean up some other instances where we are defining a new query_map
deep within the call tree.

Fixes: #847 (I hope)
Signed-off-by: Sage Weil <sage.weil@dreamhost.com>