All the acceptance tests are failing

Hi Team,

Facing below issue in v2.3.0. Things are working fine when using v2.2.6

**Issue:** All the acceptance are failing where test helpers (visit, click etc) are being used.

**Error:** `TypeError: Cannot read property 'lookup' of undefined` - in https://github.com/emberjs/ember.js/blob/master/packages/ember-testing/lib/helpers/visit.js#L22

**Reason:** As far as I have seen, application object created in `repo/tests/helpers/start-app.js` (For eg, https://github.com/emberjs/ember-test-helpers/blob/master/tests/helpers/start-app.js#L12) is not having `__container__` property (and few other props) when using v2.3.0. With v2.2.6, this is fine.

Can you help to understand what is causing this behaviour please. Am I missing something here?

I'm using Ember version: `v2.15.1`

Thanks in advance!