[SPARK-16212][STREAMING][KAFKA] use random port for embedded kafka

## What changes were proposed in this pull request?

Testing for 0.10 uncovered an issue with a fixed port number being used in KafkaTestUtils.  This is making a roughly equivalent fix for the 0.8 connector

## How was this patch tested?

Unit tests, manual tests

Author: cody koeninger <cody@koeninger.org>

Closes #14018 from koeninger/kafka-0-8-test-port.