The feature was part of the old role but unconditionally. When porting
to external role we made it optional with variable
`docker_cron_image_prune` but default to false. Restore the previous
behaviour in this playbook.
To install docker on a host you have to put it into that group in
inventory now, instead of adding the role to each host playbook. Idea
is to extend the group docker_host playbook by more docker related
things as for example metrics and monitoring.
