Settings/bug1024695 wait for keyboard settings frame

We could add comments for the workaround here.
```
/**
 * XXX: Workaround to switch to the keyboard settings frame.
 * We should use `this.client.apps.switchToApp(KeyboardApp.SETTINGS_LAUNCH_PATH)`
 * to instead of the below logic once Bug 1027994 is fixed.
 */
```