fleet failure should force a reboot or shutdown or something

[crewjam]

We had a cluster of six machines, 3 master and 3 worker. But fleetctl list-machines showed only one worker. This came recently after the failure described in #1, so it is possible that fleet died in reaction to the etcd failure.

Regardless there are classes of failure where we should reboot/terminate/bail:

• failure of fleet on a worker
• failure of etcd on a master
• ...