Before this change, we assumed data may end up in a container
once we placed a TryCall() and if gRPC send failed, we did not
retry. However, a send failure cannot result in data in a
container, since only upon successful receipt of a TryCall can
pure-runner schedule a call into a container. Here we trust
gRPC and if gRPC layer says it could not send a msg, then
the receiver did not receive it.