Provide non blocking getFlightInfo #719

 /**
   * Get information about a particular data stream.
   *
   * @param context Per-call context.
   * @param descriptor The descriptor identifying the data stream.
   * @return Metadata about the stream.
   */
  FlightInfo getFlightInfo(CallContext context, FlightDescriptor descriptor);

  /**
   *  Get information about a particular data stream.
   *  
   * @param context Per-call context.
   * @param descriptor The descriptor identifying the data stream.
   * @param listener An interface for sending data back to the client.
   */
  default void getFlightInfo(CallContext context, FlightDescriptor descriptor, StreamListener<FlightInfo> listener ){
    FlightInfo flightInfo = getFlightInfo(context, descriptor);
    listener.onNext(flightInfo);
    listener.onCompleted();
  }

  /**
   *
   * @return true if blocking (default) version of getFlightInfo needs to be used by FlightService.
   */
  default boolean isBlockingFlightInfo() {
    return true;
  }