PG: choose_acting needs the value of the osd, not its index
PG: choose_acting needs the value of the osd, not its index

This caused two osds to keep flipping the acting set between [2] and
[0,2] when osd.0 was far behind and needed a backlog. This is visible
as toggling between peering and peering+degraded.

Signed-off-by: Josh Durgin <51652c783f70f5b272ebd02f1fd20d3af7a2449f@dreamhost.com>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph