Automatically restart RelocateShard if it taking too long to complete MoveKeys

It is possible for a shard relocation to get stuck if one of the destination servers cannot complete the fetch keys. If the destination server completely dies, the algorithm will re-issue the movement to a new location, but if the destination server is just really slow the movement will never complete.

If a relocation is taking too long, we should try moving the shard to a different destination team.