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1. Set message.format.version=0 on brokers. (Broker will write MessageAndOffset V0 to disk)
2. Create internal ApiVersion 0.9.0-1** which uses ProducerRequest V2 and FetchRequest V2.
3. Configure the broker to use ApiVersion 0.9.0 (ProduceRequest V1 and FetchRequest V1).
4. Do a rolling upgrade of the brokers to let the broker pick up the new code supporting ApiVersion 0.9.0-1.
5. Bump up ApiVersion of broker to 0.9.0-1. to let the broker use FetchRequest V2 for replication.
6. Upgraded brokers support both ProducerRequest V2 and FetchRequest V2 which uses magic byte 1 for MessageAndOffset.
   
   1. When broker sees a producer request V1 (MessageAndOffset = V0), it will decompress the message, assign offsets using absolute offsets and re-compress the message.(This is no worse than what the brokers are currently doing.)
      
   2. When broker sees a producer request V2 (MessageAndOffset = V1), it will decompress the message, assign offsets using absolute offsets and do re-compression.  i.e. down-convert the message format to MessageAndOffset V0.(This is no worse than what the brokers are currently doing.)
   3. When broker sees a fetch request V1 (Supporting MessageAndOffset = V0), because the data format on disk is MessageAndOffset V0, it will use the zero-copy transfer to reply with fetch response V1 with MessageAndOffset V0.
      
   4. When broker sees a fetch request V2 (Supporting MessageAndOffset = V0, V1), because the data format on disk is MessageAndOffset V0, it will use zero-copy transfer to reply with fetch response V2 with MessageAndOffset V0.
      
7. Upgrade consumer to send FetchRequest V2.
8. Upgrade producer to send ProducerRequest V2.

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