scoutfs_item_create() hasn't been working with lock coverage. It
wouldn't return -ENOENT if it didn't have the lock cached. It would
create items outside lock coverate so they wouldn't be invalidated and
re-read if another node modified the item.
Add a lock arg and teach it to populate the cache so that it's correctly
consistent.
Signed-off-by: Zach Brown <zab@versity.com>