revised answer: What you're looking to do is not possible in Worklight 6.0.0.0. It was added as part of the Worklight 6.0.0.1 fix pack release via:
PM98052 You cannot deploy with ANT tasks when security is enabled for the Application Center or Console
Make sure you are using the latest Worklight 6.0.0.x fix pack, currently: Worklight 6.0.0.2 Developer Edition (if you are an IBM customer or business partner, you can get it from Fix Central).