xfs/005: filter _scratch_mount output to match golden image

xfs/005: filter _scratch_mount output to match golden image

Failure message of mount has been changed since util-linux v2.21, to
something like:

mount: mount /dev/sda5 on /mnt/scratch failed: Structure needs cleaning

Filter the output to match the golden image for newer mount binary so
that both old and new version of mount work correctly.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>