Restrict libvirt VM ping check to IPv4
Restrict libvirt VM ping check to IPv4

The Libvirt plugin currently does not differentiate between IPv4
and IPv6 addresses, so since the 'ping' and 'fping' commands lack
IPv6 support, ping checks against v6 addresses will fail.  Adding
IPv6 support would likey first require verification that 'ping6' or
'fping6' commands exist on the host, but that will be pursued as a
future enhancement.  In the meantime, this change will restrict ping
tests to IPv4 only.

Change-Id: Icbc6281994cb5b4087e56376f47d3954e1c50c04

sapcc/monasca-agent,sapcc/monasca-agent,sapcc/monasca-agent