No longer special case app init for testing:

https://github.com/emberjs/ember.js/blob/master/packages/ember-application/lib/system/application.js#L313 actually makes app boot deterministic.
Having app boot deviate needlessly between test and prod, is likely to introduce more issues.

I stumbled into some of these issues while upgrading ember-data's test ember to ember#master.

thoughts/concerns/feedback?