[train][goal] Define new 'trove-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 'trove-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
- 'trove-tempest-ipv6-only' will run the tests.

Story: #2005477
Task: #35937

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

Change-Id: Ia247e3f22d1791c1b910f702781e7c5968c925db

.zuul.yaml

@@ -7,19 +7,22 @@
       jobs:
         - python-troveclient-tempest-neutron-src
         - trove-tempest-plugin
+        - trove-tempest-ipv6-only
     gate:
       queue: trove
       jobs:
         - python-troveclient-tempest-neutron-src
         - trove-tempest-plugin
+        - trove-tempest-ipv6-only
 - job:
     name: trove-tempest-plugin
     parent: devstack-tempest
-    required-projects:
+    required-projects: &base_required_projects
       - openstack/neutron
       - openstack/trove
       - openstack/trove-tempest-plugin
-    vars:
+      - openstack/tempest
+    vars: &base_vars
       tox_envlist: all
       devstack_localrc:
         TEMPEST_PLUGINS: /opt/stack/trove-tempest-plugin
@@ -29,3 +32,11 @@
         tempest: true
         tls-proxy: false
       tempest_test_regex: ^trove_tempest_plugin\.tests
+
+- job:
+    name: trove-tempest-ipv6-only
+    parent: devstack-tempest-ipv6
+    description: |
+      Trove devstack tempest tests job for IPv6-only deployment
+    required-projects: *base_required_projects
+    vars: *base_vars