code: static ChannelBuffer createHandshakeMessage(String serverId, ObjectMapper mapper) throws JsonProcessingException {
          return ChannelBuffers.wrappedBuffer(mapper.writeValueAsBytes(new Handshake(serverId)));
      }
docs: Create a {@code RaftNetworkClient} handshake message.
  
  @param serverId unique id of the Raft server (sent in the handshake message)
  @param mapper instance of {@code ObjectMapper} used to map handshake properties to
  their corresponding fields in the encoded handshake message
  @return {@code ChannelBuffer} instance that contains the encoded handshake message
  @throws JsonProcessingException if the handshake message cannot be constructed