overlay: test chattr lower file in overlay

overlay: test chattr lower file in overlay

chattr with [iap..] attributes open file for read-only and invoke
ioctl(). If we chattr a lower file in overlay, it will get the lower
file but not trigger copy-up, so ioctl() lead to modification of
that lower file incorrectly. Add this test for this case.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>