Make ping test support older overcloud release.
Make ping test support older overcloud release.

In mixed version test scenario, we can have a ping test triggered
after the overcloud installation just to make sure that it works.

If we fix the version to queen then this scenario cannot work.

Change-Id: Ifdc0531cdba03af63231d3c3b16f59e4e22ec837

dprince/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,openstack/tripleo-heat-templates