CI: enable libvirt TLS in TLS jobs

Enable libvirt TLS in CI jobs with TLS enabled.

Uses the new functionality of the certificates command to generate
certificates for both libvirt client and server (added in
I1bde9fa018f66037aec82dc74c61ad1f477a7c12).

Change-Id: Ica304685b043f699799ccee6c9c2fbcf968888db

tests/templates/globals-default.j2

@@ -146,6 +146,8 @@ openstack_cacert: "/etc/pki/tls/certs/ca-bundle.crt"
 {% endif %}
 kolla_admin_openrc_cacert: "{% raw %}{{ kolla_certificates_dir }}{% endraw %}/ca/root.crt"
 rabbitmq_enable_tls: "yes"
+# TODO(mgoddard): Set this to "yes" when previous release is Yoga.
+libvirt_tls: "{{ not is_upgrade or previous_release != 'xena' }}"
 {% endif %}
 
 {% if scenario == 'linuxbridge' %}