Setup framework for IPv6-only deployment verification

Devstack IPv6 base job 'devstack-IPv6' setup the IPv6 setting
to deploy the services to listen on IPv6 address.

Tempest 'devstack-tempest-ipv6' job derived from 'devstack-IPv6'
job adds the playbooks to run the tests.

As part of Train community goal 'Support IPv6-Only Deployments',
we will expand the 'devstack-tempest-ipv6' job to do
IPv6-only deployments verification.

This commit define the new roles of 'ipv6-only-deployments-verification'
which will be invoked as part of run phase of 'devstack-tempest-ipv6' job.
This role will do IPv6-only setting and deployments verification via
tools/verify-ipv6-only-deployement.sh

IPv6 verification script can be extended further to perform more checks
and via project specific test case. Those tests will run as part of project
specific child jobs.

The 'devstack-tempest-ipv6' job will be used as parent for project specific
IPv6-only job. Those child job can extend the project specific IPv6 verification
by defining new playebook for post-run. That way the base verification
done in 'devstack-tempest-ipv6' will still run in addition to project specific
verificaiton and tests run.

Verification structure will be:
- 'devstack-IPv6' deploy the service on IPv6
- 'devstack-tempest-ipv6' run will verify the IPv6-only setting and listen address
- Child jobs derived from 'devstack-tempest-ipv6' will run the IPv6 related test case or
  any further IPv6 deployment verification.

This commit also adds the new job 'tempest-ipv6-only' which will run smoke
and ipv6 related tests present in Tempest. This job will be used to run
on 6 services (Nova, Neutron, Cinder, Keystone, Glance, Swift) deployed
by devstack.

Story: #2005477
Task: #35923

Change-Id: Ie1e5e5e02ee45ab7a4aae0f35bdb42afc2c3fe2e
diff --git a/tox.ini b/tox.ini
index 8a7a509..53d7355 100644
--- a/tox.ini
+++ b/tox.ini
@@ -231,6 +231,18 @@
     find . -type f -name "*.pyc" -delete
     tempest run --serial --regex '\[.*\bslow\b.*\]' {posargs}
 
+[testenv:ipv6-only]
+envdir = .tox/tempest
+sitepackages = {[tempestenv]sitepackages}
+setenv = {[tempestenv]setenv}
+deps = {[tempestenv]deps}
+# Run only smoke and ipv6 tests. This env is used to tests
+# the ipv6 deployments and basic tests run fine so that we can
+# verify that services listen on IPv6 address.
+commands =
+    find . -type f -name "*.pyc" -delete
+    tempest run --regex '\[.*\bsmoke|ipv6|test_network_v6\b.*\]' {posargs}
+
 [testenv:venv]
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}