osd/ReplicatedPG: handle promotion of rollback, src_oids, etc.

osd/ReplicatedPG: handle promotion of rollback, src_oids, etc.

Make other find_object_context() callers handle the case where the object
in question needs to be promoted.  We add a flag here that forces a promote
for these secondary objects so that the entire operation happens in the
same pool.  Forwarding is not allowed in this case.

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