xfstests: ln failure output has changed again

xfstests: ln failure output has changed again

Recent coreutils packages have changed the failure output of ln(1)
(again!) to be more verbose, breaking the filter in test 103:

-ln: creating symbolic link `SCRATCH_MNT/nosymlink/target' to `SCRATCH_MNT/nosymlink/source': Operation not permitted
+ln: failed to create symbolic link `SCRATCH_MNT/nosymlink/target' to `SCRATCH_MNT/nosymlink/source': Operation not permitted

Fix it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>