hg: jdk/sandbox: Add missing TestUtils class for testing onError

[erik.gahlin at oracle.com]

Changeset: 9b4841a568cb
Author:    egahlin
Date:      2019-09-27 13:01 +0200
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/9b4841a568cb

Add missing TestUtils class for testing onError

+ test/jdk/jdk/jfr/api/consumer/recordingstream/TestUtils.java