Adding ability to run a single sub-test for tests under jtreg.

[jlahoda]

New versions of jtreg (the test framework for OpenJDK) support running a single test method. This patch adds support for this for junit, testng and javac's internal framework TestRunner, to run individual test methods. It also fixes some problems found along the way: JUnit 5 support for jtreg tests, test method inside a class marked as test are recognized for TestNG.

---

^Add meaningful description above

By opening a pull request you confirm that, unless explicitly stated otherwise, the changes -

• are all your own work, and you have the right to contribute them.
• are contributed solely under the terms and conditions of the Apache License 2.0 (see section 5 of the license for more information).

Please make sure (eg. git log) that all commits have a valid name and email address for you in the Author field.

If you're a first time contributor, see the Contributing guidelines for more information.

If you're a committer, please label the PR before pressing "Create pull request" so that the right test jobs can run.

[mbien]

looks good to me

we might want to integrate #6194 first, since it enables some tests which would give this better coverage

[mbien]

going to resolve merge conflict in project.xml locally, force push and merge once green again