FLUME-3327 add useKafkaHeader option to convert flume headers as kafk…

[stakafum]

…a ones transparently in KafkaSource,

KafkaChannel, and KafkaSink

[slem1]

+1 for this feature ^^

[kamazee]

Is there a chance for it to get in if all the comments are addressed?

[bessbd]

Is there a chance for it to get in if all the comments are addressed?

I don't have the time and resources to do a proper review here, but when the comments are addressed and @tmgstevens approves the change, then I don't see why not.

[tmgstevens]

Yes, I'm happy to push this once the comments have been resolved.

[rgoers]

This has conflicts with the patch I just applied for FLUME-3435 which adds support for the timestamp and headers to KafkaSink and KafkaSource. I did not add them to KafkaChannel as I wasn't sure if the semantics should be the same.