Make project.properties path independent per API (#1863)
Make project.properties path independent per API (#1863)

- Previously we generate all project.properties files into root which is
incorrect
- Now the caller API client needs to pass in package path to retrieve the
corresponding version
- Create project.properties for Veneer-only clients as well


googleapis/google-cloud-java,googleapis/google-cloud-java,googleapis/google-cloud-java