Make some tests more robust wrt building with old libvirt
Make some tests more robust wrt building with old libvirt

The GetAllDomainStats and ListAllInterfaceAddresses methods
are only available with certain libvirt versions, so we must
cope with an error being raised.

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

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