overlay: fix exit code for some fsck.overlay valid cases

overlay: fix exit code for some fsck.overlay valid cases

Some valid test cases about fsck.overlay may be not valid enough now,
they lose the impure xattr on the parent directory of the simluated
redirect directory, and lose the whiteout which use to cover the origin
lower object. Then fsck.overlay will fix these two inconsistency which
are not those test cases want to cover, thus it will lead to
fsck.overlay return FSCK_NONDESTRUCT instead of FSCK_OK. Fix these by
complement the missing overlay related features.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>