Variable `docker_stack_files_dir` can be used if other stack deployments
need to copy over configuration files or other extra files. Defaults to
`/stacks` but can be set to anything and other roles should take care to
respect this and put their files relative to it.
Variable `docker_swarm_public_network_name` can be used to set the name
of the network to be created that faces outwards (ingress network) and
to which all stacks will be connecting.
