For chroot connection (e.g. when building images instead of working on
live hosts) one cannot restart services etc.
Also due to Ansible bug 21026 one must run systemctl instead of using
the service module, limiting support to EL 7 for the time being.
ansible_virtualization_type is undefined in Ansible > 2.5 when no virtualization
is used. A jinja2 filter has been added that provides a default value (None) so
that the check does not fail
This uses the validate option to check the config file early, which
avoids putting bad settings in place at all, and also enables a
fail-fast behaviour (errors out when processing the template module).
