My personal recommendation:
- If those “oc_test” DB user you have can be removed (not being used, only by this ownCloud), then remove them.
- When you’re setting up the DB connection, use the DB root account. In case of MySQL, ownCloud will try to create the DB and a new DB user with the required permissions over that DB. Note that ownCloud will access with this new user, not with the root account (you can recheck in the config.php file once the setup process finishes.