python release v3.0.0b2.post1 breaks gcloud-python

See: https://github.com/GoogleCloudPlatform/gcloud-python/issues/1570

Probable cause: https://github.com/google/protobuf/commit/786f80fe6632902be74f90a577d75e8641494abd#commitcomment-16491845

@haberman @silviulica 
