Make interface stats test more robust
Make interface stats test more robust

Check whether the 'default' virtual network exists and is
running before trying to use it.

Use a fixed vnet name to avoid clashes with other running
VMs on the host (if any).

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

libvirt/libvirt-go,libvirt/libvirt-go,libvirt/libvirt-go,libvirt/libvirt-go