Add sharded rollback tests

We don't do any testing specifically of rollbacks in sharding. Sharding can do special writes so we should make sure they get timestamped and rolled back correctly. A sharded rollback fuzzer that adds sharding metadata commands to the grammar would be interesting. A sharded kill_nodes suite that kills primaries and secondaries in config servers and shards would also be useful. Simply doing a sharded kill_primaries or kill_secondaries suite would go a long way.