* gnu/installer/parted.scm (&cannot-read-uuid): New condition.
(cannot-read-uuid?, cannot-read-uuid-partition): New procedures.
(check-user-partitions): Check that all user-partitions have a valid UUID,
raide the above condition otherwise.
* gnu/installer/newt/partition.scm (run-disk-page): Run an error page if the
&cannot-read-uuid condition is raised.