mkfs.ubifs: do not override root inode permissions

mkfs.ubifs: do not override root inode permissions

When mkfs.ubifs is used with -r dir, it does not make the root UBIFS
inode uid/gid/permissions to be equivalent to dir's permissions, but
it makes root inode permissions to be equivalent to uid = git = 0
(root) and permissions = u+rwx go+rx.

Unfortunately, we cannot simply fix this bug, because mkfs.ubifs is
already used in production. Thus, we have introduce --squash-rino-perm
option which is the default and it preserves the old mkfs.ubifs
behavior. We also introduce --nosquash-rino-perm option which fixes
mkfs.ubifs behavior. If none of these options is used, we print a
warning. The plan is to make everyone use one of these options, then
make --nosquash-rino-perm to be the default and remove the warning,
and then eventually deprecate and remove both options.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>