Fix the test module for mocking mojit models.


With this fix, apps can test their models, which are now accessed via the `ac.models` addon, like this:
```
var ac = new Y.mojito.MockActionContext({
    addons: [ 'http' ],
    models: [ 'foo' ]
});

ac.models.get('foo').expect({
    method: 'getData',
    args: ...
});

controller.index(ac);

// somewhere in controller
ac.models.get('foo').getData(....);
```