Active app port is assumed to be the app to test

[minkimcello]

If another app is opened in the same port that is configured to be the app port in bigtest.json, the server will assume it's the app that it's supposed to test. But if the app.command is configured, I think we should have it check if it's already active or not.

The sample app opens in port 3000 by default and I noticed if I run bigtest with the sample app while I'm working on the bigtest website (which also uses port 3000), bigtest will run the sample app tests against the bigtest website.

[cowboyd]

This makes a lot of sense. We need to re-think out our port mapping strategy. Some ports should be fixed and fail if the won't bind, while others need to be flexible. I'm thinking about cases where we have multiple bigtest servers running on the same system.