As a developer, I want to run validation playbooks without tearing down

[Yolanda Robla]

I'll comment my use case. We are running tripleo-quickstart in jenkins, as part of a testing pipeline.
In our case, we want to have an specific job for building the cloud, but then run different tests like tempest or rally to add validation.
The validation job that includes tempest, can fail from time to time due to temporary problems, timeouts, etc... we'd like to retry it without having the need to redeploy the full cloud.
So the idea was to run overcloud-validate playbook by separate, but then we hit that the playbook is tearing nodes by default (TEARDOWN_TAGS='teardown-nodes' by default), and there is no way to pass "teardown=none"
We need to have a way to run that isolated play without tearing down all the deployed cloud.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/335493

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/335493
Committed: https://git.openstack.org/cgit/openstack/tripleo-quickstart/commit/?id=5d9b88c231cdff64d4d0adf49869272308e525c1
Submitter: Jenkins
Branch: master

commit 5d9b88c231cdff64d4d0adf49869272308e525c1
Author: John Trowbridge <email address hidden>
Date: Wed Jun 29 09:12:26 2016 -0400

    Add ability to explicitly NOT teardown

    We added the ability to explicitly choose what to teardown, but
    did not think about the case where a user would not want to tear
    anything down. One such use case is running multiple validations
    against a deployed overcloud.

    Co-Authored-By: Attila Darazs <email address hidden>
    Change-Id: I2d9be4069cdc298a5151bd190b696269e971b94c
    Closes-Bug: 1597331