Major Description
Have a periodic mechanism to delete state=INACTIVE shards. The implementation is a ClusterSingleton.
Original title: SPLITSHARD should delete the parent shard after success
Original description:
When a shard is split into two sub-shards, the parent (the original) will remain in an "INACTIVE" state. It's up to the user/admin to devise some clean-up process. I propose that SplitShardCmd clean up after itself. It's not clear why it didn't do this all along.
