This would previously result in
nova.virt.libvirt.host.Host.has_min_version not being correctly mocked
and would instead rely on the versions of libvirt and QEMU being
reported by FakeLibvirt being lower than
MIN_LIBVIRT_VIDEO_MODEL_VERSIONS['none'] aka libvirt v4.6.0.
Change-Id: I4624ff7dd1e71c8a9656e4ce2118fd04941a4086