Have NPX start server before running the transform.

[tylerturdenpants]

If the NPX can find /app (and maybe some other key files to confirm its an ember project) we should start the application for the user instead instructing the user to do it.

One caveat would be to make sure we don't do this on a port already in use and keep counting upwards until one is free.

[ghost]

I'd vote hinting based on ember-cli-build.js.
This starts the ember server right? If so you can use ember serve --port 0 as that will find an available port.