add wrapper for grpc.Server.wait_for_termination

[william-plano-oxb]

Hi, grpc/grpc#19299 added a handy wait_for_termination method to the grpc.Server interface.
It would be cool to implement this in _InterceptorServer and pass through to the underlying server.
...
Though looking at it, I think #14 will resolve this since it removes the wrapped server entirely. Is there an ETA on that PR at all?

[inquire]

Hi, i agree with @william-plano-oxb getting rid of the wrapper on that interface should make things a lot better and allow for the wait_for_termination problem. Anything we can help with to get this process over the line?