Exclude test-sources.jar when $INCLUDE_TEST_JARS is FALSE Author: Magesh Nandakumar <magesh.n.kumar@gmail.com> Reviewers: Konstantine Karantasis <konstantine@confluent.io>, Robert Yokota <rayokota@gmail.com>, Arjun Satish <arjun@confluent.io>, Randall Hauch <rhauch@gmail.com>, Ewen Cheslack-Postava <ewen@confluent.io> Closes #5139 from mageshn/KAFKA-6997