As suggested by Anthony, this patch and the next one were split apart.  This
patch just adds the basic plumbing to qemu to be able to set the uuid on the
command-line, and retrieve the information via "info uuid".

Signed-off-by: Chris Lalancette <clalance@redhat.com>
Cc: Gleb Natapov <gleb@qumranet.com>
Cc: Anthony Liguori <anthony@codemonkey.ws>