[train][goal] Define new 'freezer-tempest-ipv6-only' job

As part of Train community goal 'Support IPv6-Only Deployments and Testing'[1],
Tempest has defined the base job 'devstack-tempest-ipv6' which will
deploy services on IPv6.

This commit adds the new job 'freezer-tempest-ipv6-only'
run on gate which is derived from 'devstack-tempest-ipv6'.

Verification structure will be:
- 'devstack-IPv6' deploy the service on IPv6
- 'devstack-tempest-ipv6' run will verify the IPv6-only setting and listen address
- 'freezer-tempest-ipv6-only' will run the tests.

Story: #2005477
Task: #35890

[1] https://governance.openstack.org/tc/goals/train/ipv6-support-and-testing.html

Change-Id: Iad288fe17db561cf266ae3db5a66ea250fbace33

.zuul.yaml

@@ -6,6 +6,7 @@
     check:
       jobs:
         - freezer-tempest-basic
+        - freezer-tempest-ipv6-only
         - freezer-tempest-client
         - freezer-tempest-scheduler
         - freezer-tempest-agent
@@ -13,6 +14,7 @@
     gate:
       jobs:
         - freezer-tempest-basic
+        - freezer-tempest-ipv6-only
         - freezer-tempest-client
         - freezer-tempest-scheduler
         - freezer-tempest-agent
@@ -27,7 +29,7 @@
     # Victoria gate onwards.
     # nodeset: openstack-single-node-bionic
     timeout: 7200
-    required-projects:
+    required-projects: &base_required_projects
       - openstack/python-openstackclient
       - openstack/swift
       - openstack/python-freezerclient
@@ -35,7 +37,7 @@
       - openstack/freezer-api
       - openstack/freezer-tempest-plugin
       - openstack/tempest
-    vars:
+    vars: &base_vars
       devstack_localrc:
         FREEZER_BACKEND: 'sqlalchemy'
       devstack_plugins:
@@ -56,6 +58,15 @@
       zuul_copy_output:
         /etc/hosts: logs
 
+- job:
+    name: freezer-tempest-ipv6-only
+    parent: devstack-tempest-ipv6
+    description: |
+      Freezer devstack tempest tests job for IPv6-only deployment
+    timeout: 7200
+    required-projects: *base_required_projects
+    vars: *base_vars
+
 - job:
     name: freezer-tempest-client
     parent: freezer-tempest-basic