Components are always wrapped in divs, even if tagName is defined

Recreating the issue created in ember.js repo which was closed asking to open in ember-test-helpers library.
https://github.com/emberjs/ember.js/issues/12937

When a component has its `tagName` property set to anything other than div, I'd expect the rendered tag to be that specified by tagName, but instead the required form is still wrapped in a div in integration tests. Eg:

```js
// some-component.js
Ember.Component.extend({
tagName: 'form'
})
```

Expected HTML

```

```

Actual HTML

```