fix(producer): return errors for every message in retryBatch to avoid producer hang forever

[cch123]

This fixes #2377

[cch123]

CLA signed

[dnwe]

Thanks for investigating this issue and submitting the fix, this change looks good to me

[dnwe]

@cch123 do you think you might be able to add a functional test that covers this scenario?

[cch123]

@cch123 do you think you might be able to add a functional test that covers this scenario?

let me think about it.. I think the backoff param also didn't work, and need some time to find out why...

[cch123]

@dnwe PTAL

[cch123]

The backoff bug will be fixed in another PR

[dnwe]

Thanks!