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.
Docker does not take the tzdata from host systems, so the
timezone needs to be set individually.
Otherwise dates without explicit timezone information or Z will
be generated or interpreted in the wrong timezone
(such as dokuwiki signatures)
