Reuse client stub in grpsink (#487)
Reuse client stub in grpsink (#487)

Apparently this is concurrency-safe. It's also quite costly, and we will
want to move to a batched model sooner or later.
evanj/veneur,gphat/veneur,stripe/veneur,stripe/veneur,gphat/veneur,evanj/veneur,evanj/veneur,gphat/veneur