Define new 'congress-tempest-ipv6-only' job in gate

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

This commit adds the new job 'congress-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
- 'congress-tempest-ipv6-only' will run the tests.

Story: #2005477
Task: #35885

Depends-On: https://review.opendev.org/#/c/671231/

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

Change-Id: I7f3a6b0b6973b99e535dfd379a5188732529e420

.zuul.yaml

@@ -3,12 +3,12 @@
     parent: devstack-tempest
     description: |
       Congress devstack tempest tests job
-    irrelevant-files:
+    irrelevant-files: &base_irrelevant_files
       - ^.*\.rst$
       - ^doc/.*$
       - ^congress/tests/.*$
       - ^releasenotes/.*$
-    required-projects:
+    required-projects: &base_required_projects
       - name: openstack/devstack-gate
       - name: openstack/aodh
       - name: openstack/python-aodhclient
@@ -34,7 +34,7 @@
       - name: openstack/monasca-ui
       - name: openstack/python-monascaclient
     timeout: 6000
-    vars:
+    vars: &base_vars
       devstack_plugins:
         congress: https://opendev.org/openstack/congress
         heat: https://opendev.org/openstack/heat
@@ -62,6 +62,16 @@
         ENABLE_CONGRESS_Z3: true
         USE_Z3_RELEASE: 4.7.1
 
+- job:
+    name: congress-tempest-ipv6-only
+    parent: devstack-tempest-ipv6
+    description: |
+      Congress devstack tempest tests job for IPv6-only deployment
+    irrelevant-files: *base_irrelevant_files
+    required-projects: *base_required_projects
+    timeout: 6000
+    vars: *base_vars
+
 - job:
     name: congress-tempest-py2
     parent: congress-tempest-base
@@ -169,6 +179,7 @@
         - congress-tempest-replicated-postgresql
         - congress-tempest-py2-JsonIngester
         - congress-tempest-py3-JsonIngester
+        - congress-tempest-ipv6-only
         # Note: the above jobs most likely provides sufficient coverage
         # - congress-tempest-py2-postgresql
         # - congress-tempest-py3-postgresql
@@ -190,3 +201,4 @@
       jobs:
         - congress-tempest-py2-mysql
         - congress-tempest-py3-mysql
+        - congress-tempest-ipv6-only