Comment 7 for bug 1971175

Yeah, we totally need to document that in better way. As the only mention that it's supposed to be FQDN I can find here https://opendev.org/openstack/openstack-ansible/src/branch/master/etc/openstack_deploy/openstack_user_config.yml.pod.example#L33-L36

While it's not the most obvious place too look for...