test: Update the test suite to work with game creation

Previously the test script only worked when given an API endpoint for
a single game of Empires.

In this commit we bring it up to something more modern by making it
aware of the top-level APIs for creating a new game ID and then using
that game ID to talk to the Empires API.

We also revamp the test script so that it does some actual
testing. Previously, it was just a simple script for exercising
several endpoints. Now, it actually inspects responses and ensures
that things are working correctly.