xfs/096: filter out the "Discarding..." output

Latest xfsprogs mkfs.xfs prints "Discarding blocks...Done" if the
disk supports the trim. That breaks the golden image, cause
unexpected failure, so filter out it.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/xfs/096

@@ -78,6 +78,7 @@ mkfs_filter()
 	-e 's/ ftype=[01]//' \
 	-e '/^log stripe unit.*too large/d' \
 	-e '/^log stripe unit adjusted/d' \
+	-e '/Discarding/d' \
    | grep -v parent
 }