The script runs some SQL which ultimately determines the time at which the last
backup with an exit code of zero was. If there has never been a successful
backup, we ended up reporting a clear dot. Whilst this may lead to a few
transitory red dots immediately after adding a new host, I think this is
preferable to not realising for months that a host isn't being backed up!
See ticket 154527

For offline machines, use the time between last backup and last change of conn dot status to decide on backup status

Forcing arcfour causes us not to be able to back up jessie machines.