Switch to using debugreiserfs to read the UUID (#684115)

For a mounted reiserfs file system with a Nil UUID (all zeros) GParted
will display a partition specific warning.  This comes from the reiserfs
specific read_uuid() method.  Error demonstration:

    # blkid /dev/sda15
    /dev/sda15: LABEL="test-reiserfs-2" TYPE="reiserfs"
    # mount | grep sda15
    /dev/sda15 on /mnt/2 type reiserfs (rw,relatime)
    # reiserfstune /dev/sda15
    reiserfstune: Reiserfstune is not allowed to be run on mounted filesystem.

Switch to using debugreiserfs to read the UUID as it can be used on a
mounted file system.

    # debugreiserfs /dev/sda15 2> /dev/null | grep UUI
    UUID: 00000000-0000-0000-0000-000000000000

Bug #684115 - Reiserfs UUID reading issues on Fedora and CentOS