Cleanup repeated `ember-testing` test setup

Extracts Ember Test Helper setup into `setup` blocks. Rearranges
tests to better leverage `Qunit.module` setup.

Extracts repeated calls to

```js
run(function() {
  App = EmberApplication.create();
  App.setupForTesting();

  App.injectTestHelpers();
});
```
Merge pull request #9802 from seanpdoyle/test-helpers-cleanup

Cleanup repeated `ember-testing` test setup