[FEATURE ember-testing-lazy-routing]

* `setupForTesting` sets the application into testing mode (which is
  used to defer readiness.
* Adds an initializer that defers readiness if the application is in
  testing mode.
* `visit` helper has been updated to advance readiness upon first call.
* `App.reset()` now behaves the same after `setupForTesting` (in a
  deferred state).
Merge pull request #3695 from rjackson/defer_readiness_in_initializer

[FEATURE ember-testing-lazy-routing]