overlay: add fsck.overlay impure xattr test

Add fsck.overlay test case to test it how to deal with impure xattr
in underlying directories of overlayfs.

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