Flaky Test RegexSourceIntegrationTest#testRegexMatchesTopicsAWhenCreated

The RegexSourceIntegrationTest#testRegexMatchesTopicsAWhenCreated

and RegexSourceIntegrationTest#testRegexMatchesTopicsAWhenDeleted  tests use an ArrayList to assert the topics assigned to the Streams application. 

The ConsumerRebalanceListener used in the test operates on this list as does the TestUtils.waitForCondition() to verify the expected topic assignments.

Using the same list in both places can cause a ConcurrentModficationException if the rebalance listener modifies the assignment at the same time TestUtils.waitForCondition() is using the list to verify the expected topics.