code: public State command(Command command, boolean sync)
      {
          return State.valueOf(command(command.name(), sync));
      }
docs: Sends a command message to the proxy actor.
  Can be useful for programmatic interfaces.
  Does not works with commands {@link Command#CONFIG CONFIG} and {@link Command#RESTART RESTART}.
  
  @param command  the command to execute.
  @param sync     true to read the status in synchronous way, false for asynchronous mode
  @return the read state