More dynamic config fixes.

* Ensures that `AppNameENV` and `EmberENV` are setup *before* the
  vendor files have been loaded.
* Ensures that the `<base>` tag changes when the config file is updated.
* Injects the `/tests/index.html` with the `test` environment
  configuration (was previously whatever server was running).
Merge pull request #1825 from rwjblue/fix-things

More dynamic config fixes.