qom-test: Run for all available machines Get available machines via QMP instead of hardcoding a list that's perpetually out of date. Xen machines can work only when running under the Xen hypervisor. Blacklist them. Signed-off-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Andreas Färber <afaerber@suse.de>