Start server on address 0.0.0.0

When running js-test-tool on a Vagrant instance, we want to use a browser on the host machine.  By starting the server on port 0.0.0.0 instead of 127.0.0.1, we make it accessible externally.

@jzoldak please review

@andy-armstrong When this gets merged, you will need to update `edx-platform/requirements/edx/github.txt` so that you're using js-test-tool version 0.1.5