Improve Windows libvirt VM IP detection

Improve Windows libvirt VM IP detection

On some of the KVM hosts targeted by the Windows jobs, the main
interface within the VM will have a different NIC name.

Therefore, the command:
```
virsh domifaddr --source agent --interface Ethernet --full $VM_NAME
```
will not return anything, since the NIC name is not guaranteed to
have `Ethernet` name.

These changes improve how the VM IP is detected, by filtering the
guest NICs via MAC address to find the proper NIC. Furthermore, the
VM address belonging to the `default` virsh network is returned.