test(config): allow to set dynamic baseUrl beyond localhost


This change allows to run protractor's own tests using a network selenium grid.

You can now customize the `testapp/scripts/web-server.js` host name to other than *localhost* in a similar way can customize the port number to be different from *8000* e.g.

```
export HTTP_HOST=10.0.0.15
npm test
```

I need this testing feature so i can add IE to `multiConf.js` and `ciConf.js` on a future PR.