Make 'part-by-uuid' into 'disk/by-uuid' for clarity

GNU/Linux uses the convention of '/dev/disk/by-uuid/' over
'/dev/part-by-uuid/' currently used. Rather than working
against the tide, let us try to be more interoperable with userland.

You can see this usage in places like:
'contrib/lvm2/dist/udev/13-dm-disk.rules'

We also organise other cases also to result in the new layout
in the following way: /dev/disk/by-{uuid,serno,slice-uuid}/

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>