Add integration-test blueprint

```sh
$ ember g integration-test foo
version: 0.0.34
installing
  create tests/integration/foo-test.js
```

```js
import startApp from '../helpers/start-app';

var App;

module('Integration - Foo', {
  setup: function() {
    App = startApp();
  },
  teardown: function() {
    Ember.run(App, 'destroy');
  }
});

test('visiting /foo', function() {
  visit('/foo');

  andThen(function() {
    equal(currentPath(), 'foo');
  });
});
```
I think we need to `import Ember from 'ember';`.