Speech api streaming sample doesn't support python 3

[jerjou]

This is a consequence of the underlying grpc lib not supporting it yet:

grpc/grpc#282

Once grpc supports it, we should un-skip the test in speech_streaming_test

[theacodes]

@jerjou grpc should ostensibly support Python 3 now. Can we look into removing our hacks for this?

[jerjou]

I believe this was addressed in #462