Some of our scripts and templates rely on sshd listening on the
localhost addresses (e.g. the port test in monitrc). Normally this is
achieved either by having an ssh_ role assigned to the `lo` interface,
or by listening the addresses explicitly in the `listen_addresses` list.
Add an explicit test for this in case it is missing.
Change-Id: Iee409551e8237fbdec56fe33d1bb63d56d0af802