Transform this.subject in non-rendering tests

[rwjblue]

In order to allow the codemod to leave applications in a working state, we will need to provide a path away from using this.subject(). This transformation is discussed in emberjs/rfcs#232 here.

We should transform the following for singletons (e.g. everything other than model and component):

import { moduleFor, test } from 'ember-qunit';

moduleFor('service:flash', 'Unit | Service | Flash', {
  unit: true
});

test('should allow messages to be queued', function (assert) {  
  let subject = this.subject();
  // ...snip...
});

Into this:

import { module, test } from 'qunit';
import { setupTest } from 'ember-qunit';

module('Unit | Service | Flash', function(hooks) {
  setupTest(hooks);
  
  test('should allow messages to be queued', function (assert) {
    let subject = this.owner.lookup('service:flash');
    // ...snip...
  });
});

And for non-singleton's we would do:

import { moduleFor, test } from 'ember-qunit';

moduleFor('model:foo', 'Unit | Model | Foo', {
  unit: true
});

test('should allow messages to be queued', function (assert) {  
  let subject = this.subject();
  // ...snip...
});

Into:

import { module, test } from 'qunit';
import { setupTest } from 'ember-qunit';

module('Unit | Model | Foo', function(hooks) {
  setupTest(hooks);
  
  test('should allow messages to be queued', function (assert) {
    let subject = this.owner.factoryFor('model:foo').create();
    // ...snip...
  });
});