feat(driver): Add missing env variables from adapter

- Fixes #7
- Use `ROCKETCHAT_USER` and `ROCKETCHAT_PASSWORD` for default credentials
- Use `ROCKETCHAT_ROOM` for default room joins
- Use `ROCKETCHAT_USESSL` to force SSL
- `respondToMessages` now auto-joins rooms if not yet joined
- Fix some interface / schema errors
- Add pre-test checks for instance readiness
- Add tests for all of the above