LU-11838 scrub: handle s_uuid change to uuid_t

LU-11838 scrub: handle s_uuid change to uuid_t

The 4.12 kernel changed the s_uuid field in struct super_block from
an character array to an uuid_t. While ldiskfs uses it own s_uuid
field in struct ext4_super_block that field is a char array instead
of an uuid. Currently on going effort are being down in the linux
kernel to move to uuid_t so I suspect this will change in the future.
Since this is the case change all the character arrays for uuid
handling to uuid_t located in the scrubbing code. Change osd-ldiskfs
to use the struct super_block uuid, which is equivalent to s_es
version, to handle the uuid_t changes now.

Change-Id: I40643d342b5bc17a6ef922e99b3e8524930822de
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/34689
Tested-by: Jenkins
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>