osd/PG: normalize query processing in Stray and ReplicaActive

osd/PG: normalize query processing in Stray and ReplicaActive

A stray PG may end up in ReplicaActive if it is participating in backfill.
However, whether it is or isn't, we should treat queries the same.
Otherwise we end up with weird behaviors like:

 - osd's stray pg moves to ReplicaActive (gets info+log from primary)
 - osd goes down and back up
 - primary restarts peering, request FULLLOG to find missing objects
 - osd ignores FULLLOG because it is ReplicaActive and not Stray

Fixes: http://tracker.ceph.com/issues/24373
Reported-by: Kouya Shimura <kouya@jp.fujitsu.com>
Signed-off-by: Sage Weil <sage@redhat.com>