Do not use global Promise when it is Ember.RSVP.Promise.
Do not use global Promise when it is Ember.RSVP.Promise.

This ensures that when folks do something like this:

```js
if (typeof Promise === 'undefined') {
  self.Promise = Ember.RSVP.Promise;
}
```

We still use a Promise that is **not** configured on the run loop.

switchfly/ember-test-helpers,switchfly/ember-test-helpers