I've found that given a sufficiently bad replica2part2dev table we can
accidently not entirely fix palcement when more than two replicas of a
part are assigned to the duplicate devices.
It shows up most on > 3 replica rings when you have two *different*
devices both holding two replicas. But you can see it on a three
replica ring when all three replicas are assigned to the same device.
Change-Id: Ieb213c1a259815a2ed657291242919cda568c7b5
b19dc1ddec