If our chosen backup repo is a local one, each restic container needs to
mount the local path as a volume, otherwise the data is stuck in the
container itself.
Will pass through the hostname to any snapshots set up.
The hostname is _not_ derived from the random docker container string
but instead takes the name of the _host_ on which docker is running
(from ansible facts).
The hostname in combination with the tag should point to the correct
host -> stack which is being backed up.
