reuse topicdata when sending producerrequest

The way that SyncProducer sends a ProducerRequest over socket is to first serialize the whole request in a bytebuffer and then sends the bytebuffer through socket. An alternative is to send the request like FetchReponse, using a ProduceRequestSend that reuses TopicDataSend. This avoids code duplication and is more efficient since it sends data in ByteBufferMessagesSet directly to socket and avoids extra copying from messageset to bytebuffer.