RFR: 8306711: Improve diagnosis of `IntlTest` framework

[Justin Lu]

Please review changes to the IntlTest (test framework) class. 

These changes include
- Logging the actual exception + stack trace. Previously, the test framework would throw `InvocationTargetException` but hide the actual underlying exception of the failing test unless the test class was ran with -nothrow.
- Sorting the tests, ensuring for any given run, the tests are ran in the same order. (In [JDK-8305853](https://bugs.openjdk.org/browse/JDK-8305853) it was discovered that on Windows, the test framework would execute tests in a random order each time).
- Removing unused methods + improving output.

-------------

Commit messages:
 - Exc changes, sort tests, general cleanup

Changes: https://git.openjdk.org/jdk/pull/13655/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13655&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306711
  Stats: 118 lines in 1 file changed: 44 ins; 59 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/13655.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13655/head:pull/13655

PR: https://git.openjdk.org/jdk/pull/13655