hack(server): notify removed peers when they try to become candidates

A peer might be removed during a network partiton. When it comes back it
will not have received any of the log entries that would have notified
it of its removal and go onto propose a vote. This will disrupt the
cluster and the cluster should give the machine feedback that it is no
longer a member.

In reaction to this notification the machine should shutdown. In this
case the shutdown just moves it towards becoming a standby server.