If the following events were to occur, resharding would incorrectly fail
(1) Suppose the donor is a recipient as well as donor and in kBlockingWrites
(2) The donor renames the collection - no more temporaryNss collection
(3) Before it can persist its decision to kDone, a failover occurs
(4) Donor steps up, still in kBlockingWrites
(5) The donor tries to rename the temporary collection again. it fails with NamespaceNotFound since the temporaryNss was already renamed before the failover.