Join request from leader is proxied back to itself

[kuujo]

When servers start up, the first thing they always do is send a JoinRequest to any node that can handle it. But the logic for joining the cluster is independent of server states. So, when a server starts and is elected leader, it will often attempt to join through another node which will proxy the join back to the leader. This is obviously just an odd behavior. The join logic should recognize the local server as the leader and complete the join with no configuration change.