CODETOOLS-7902003 added a unique test.classes directory for each test, behavior which is incompatible w/a few existing tests. According to the announcement email for jtreg4.2-b08, http://mail.openjdk.java.net/pipermail/jtreg-use/2017-July/000579.html:

"... the new behavior is only enabled for test suites that explicitly request the use of "jtreg 4.2 b08" or later, in the requiredVersion property in TEST.ROOT."

However, the feature is enabled if the test suite has no requiredVersion property set. This prevents jtreg4.2-b08 from being used with jdk8u.