Buggy test initialization

The test initializer was not up to date with [Ember Integration Testing Official Guide](http://emberjs.com/guides/testing/integration/). 

* Calls like `Ember.run` caused troubles while writing integration tests
* Test container creation in `_initializer.coffee` was not aligned with `_initializer.js`
* `Ember.testing = true` is useless, since `setupForTesting` handles everything for you