This commit allows the model to fetch IPv6 addresses
from running VMs and populate VirtualMachine objects
with the value if it was retrieved successfully
The shell script which gets informations from libvirt incorrectly
matches virsh output lines which contain VMs' public IPv4 addresses.
It doesn't work when there are multiple address families which breaks
reporting of IPv4 address when a VM also has an IPv6 address and virsh
happen to output that one first.
This commit changes it to explicitely match the first ipv4 address instead.
