Change the inclusion of backup containers so they actually work. They
check that restic is enabled globally, and that restic is enabled for
the individual stack they belong to. If either of the conditions is not
met they do not deploy.
This way we can simply enable restic globally with `restic_enable` and
by default all stacks will be backed up. But if we want to exclude
specific stacks from backups we can do so with the individual
`<role>_restic_enable = False` variable.
Finally found a good version of doing so with the help of the following
medium article: https://medium.com/opsops/is-defined-in-ansible-d490945611ae
which basically makes use of default fallbacks instead.
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.
