ember-source@3 + ember-cli@3 does not generate valid tests

[nathanhammond]

As of ember-cli/ember-cli#7546 landing, we no longer have any helpers in Ember CLI.

This breaks the blueprints for instance-initializers and initializers.

It also is broken for Mocha acceptance tests:
https://github.com/emberjs/ember.js/blob/master/blueprints/acceptance-test/mocha-files/tests/acceptance/__name__-test.js

(I'm not sure that I've enumerated everywhere that it fails.)

This bug is effectively a duplicate of #16180, but exists because #16229 is incomplete.

[rwjblue]

@nathanhammond - RE: the Mocha point: ember-mocha re-regenerates the start-app and destroy-app helpers (because it isn't quite finished with support for the newer testing system).

[Serabe]

Thank you!