I made a mistake in #24398. The grpc.aio fix isn't working after the roll back, because the __name__ of the __init__.py file of gRPC Python module is "grpc" instead of grpc.__init__. So, it won't load "aio" module under any setup by default.

The init_test wasn't testing direct import of "grpc.aio", because it takes a dependency on AioTestBase which does from grpc import aio. The module space is still polluted, so the test didn't caught the error.

Here is the cherry-pick for google3 (cl/335987017).