refactor 4+6 to use alt image with ipv6 support after review
refactor 4+6 to use alt image with ipv6 support after review

Change-Id: I14eab909445446ed36e1109d20f4ee669b8502ac

cisco-openstack/tempest,cisco-openstack/tempest,CiscoSystems/tempest,CiscoSystems/tempest