message: network-grpc: API to poll client for readiness
  It is necessary to poll for the client connection object for readiness,
  otherwise requests issued concurrently may fail.
diff: @@ -310,6 +310,18 @@ where
  }
  req
  }
  +
  + pub fn poll_ready(&mut self) -> Poll<(), core_error::Error> {
  + self.service.poll_ready().map_err(error_from_grpc)
  + }
  +
  + pub fn ready(self) -> impl Future<Item = Self, Error = core_error::Error> {
  + let node_id = self.node_id;
  + self.service
  + .ready()
  + .map(move |service| Connection { service, node_id })
  + .map_err(error_from_grpc)
  + }
  }
  impl<P> P2pService for Connection<P>
  