Remove UUID from root device hints
Remove UUID from root device hints

It's only possible to get an UUID from a partition fileystem, not from
a disk device.

Change-Id: Id486c529c795bbc2ccbe747d21183a0e53d83df7

openstack/ironic-specs,bcornec/ironic-specs,NaohiroTamura/ironic-specs,naterh/ironic-specs