Monitor etcd connectivity

Since the heartbeat provides presence information, a failed heartbeat means the fleet server is no longer able to operate in the cluster. The Heart and Monitor pieces are now responsible for the Machine heartbeat. The Monitor provides a trigger for stopping, purging, and starting the fleet server in response to a failed heartbeat.
```
// Monitor tracks the health of the Server. If the Server becomes unhealthy, 
// it is stopped and restarted
```

or something