Update switching forms test
Update switching forms test

- simpler call to PolicyPrediction, using all defaults
- Build up an `events_expected` list as we go, and assert it against the tracker
- Include the `BotUttered()` event in the `events_expected` list that is asserted.
RasaHQ/rasa_nlu,RasaHQ/rasa_nlu,RasaHQ/rasa_nlu