qdev-properties: add UUID property type

qdev-properties: add UUID property type

UUIDs (GUIDs) are widely used in VMBus-related stuff, so a dedicated
property type becomes helpful.

The property accepts a string-formatted UUID or a special keyword "auto"
meaning a randomly generated UUID; the latter is also the default when
the property is not given a value explicitly.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>