RFR: 7904125: JUnit test discovery issues must result in jtreg test failure

[Jaikiran Pai]

Can I please get a review of this change which proposes to fail a jtreg test if there were  any junit test engine discovery errors? This addresses https://bugs.openjdk.org/browse/CODETOOLS-7904125.

This change should prevent issues like https://bugs.openjdk.org/browse/JDK-8374434 where the warning is being logged by junit but they go unnoticed because there's no test failure raised for those issues.

A new self test has been introduced to reproduce the issue and verify the change.

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Commit messages:
 - copyright year
 - add code comment
 - add self test
 - 7904125: Report JUnit issues encountered during test discovery

Changes: https://git.openjdk.org/jtreg/pull/304/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=304&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904125
  Stats: 105 lines in 4 files changed: 104 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/304.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/304/head:pull/304

PR: https://git.openjdk.org/jtreg/pull/304