btrfs/004: fix to make test really work

btrfs/004: fix to make test really work

So I was wondering why test 004 could pass my previous wrong
kernel patch while it defenitely should not.

By some debugging, i found here perl script is wrong, we did not
filter out anything and this unit test did not work acutally.so
it came out we will never fail this test.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>