[SPARK-16212][STREAMING][KAFKA] apply test tweaks from 0-10 to 0-8 as well

## What changes were proposed in this pull request?

Bring the kafka-0-8 subproject up to date with some test modifications from development on 0-10.

Main changes are
- eliminating waits on concurrent queue in favor of an assert on received results,
- atomics instead of volatile (although this probably doesn't matter)
- increasing uniqueness of topic names

## How was this patch tested?

Unit tests

Author: cody koeninger <cody@koeninger.org>

Closes #14073 from koeninger/kafka-0-8-test-direct-cleanup.