re-adding member to replica set without keyFile results in secondary node

If a replica set is started with authentication via a key file, and a member is shut down and restarted without a key file, the member will eventually rejoin the replica set and become a SECONDARY member, even though (it appears) that the oplog and database are empty. Queries could get routed to these nodes with weird effects.

Invalid key files result in a RECOVERING state, which is probably correct.