infra-journal-remote: Skip playbook on empty emtpy log_hosts group
infra-journal-remote: Skip playbook on empty emtpy log_hosts group

If the log_hosts group is empty, then the deployment fails with the
following error:

{{ hostvars[groups['log_hosts'][0]]['ansible_host'] }}: list object has no element 0"}

As such, we need to skip the playbook if no hosts are defined in that
group.

Change-Id: Icf528f8c71e61de9e5a4c1e4004f5b269508d051

stackforge/os-ansible-deployment,stackforge/os-ansible-deployment,openstack/openstack-ansible,openstack/openstack-ansible,bunchc/openstack-ansible,bunchc/openstack-ansible