generic: test i_mode recovery after power failure

generic: test i_mode recovery after power failure

After fsync, filesystem should guarantee inode metadata including
permission info being persisted, so even after sudden power-cut,
during mount, we should recover i_mode fields correctly, in order
to not loss those meta info.

So adding this testcase to check whether generic filesystem can
guarantee that.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>