fixed ping vnf support ipv6
fixed ping vnf support ipv6

Now monitor the VNF. If the VNF address is IPV6,
it cannot use 'ping', should use ping6.

Change-Id: I7e7303bf1ee6c2e0c2995010564a93943aaacc49

stackforge/tacker,openstack/tacker,openstack/tacker,stackforge/tacker,openstack/tacker