[jdk21u-dev] RFR: 8332885: Clarify failure_handler self-tests

[Martin Doerr]

Clean backport of [JDK-8332885](https://bugs.openjdk.org/browse/JDK-8332885).

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Commit messages:
 - Backport 08891553bbd3d71337d8a94c75051db74e15903f

Changes: https://git.openjdk.org/jdk21u-dev/pull/658/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=658&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332885
  Stats: 16 lines in 2 files changed: 16 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/658.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/658/head:pull/658

PR: https://git.openjdk.org/jdk21u-dev/pull/658