Bug 1069184 - [ftu] unittest navigation_test.js incorrect using assert.include for testing existing object property

```javascript
178: Navigation.forward();
     assert.include(UIManager.finishScreen.classList, 'show');
     assert.isFalse(UIManager.activationScreen.classList.contains('show'));
```

assert.include - test inclusion of an object in another. Works for strings and Arrays, for other do nothing!! You may set any string - draft_draft for example and test OK!