## What changes were proposed in this pull request?

Put Kafka 0.8 support behind a kafka-0-8 profile.

## How was this patch tested?

Existing tests, but, until PR builder and Jenkins configs are updated the effect here is to not build or test Kafka 0.8 support at all.

Author: Sean Owen <sowen@cloudera.com>

Closes #19134 from srowen/SPARK-21893.