[jdk17u-dev] RFR: 8315766: Parallelize gc/stress/TestStressIHOPMultiThread.java test

[Soumadipta Roy]

Backporting the fix for https://bugs.openjdk.org/browse/JDK-8315766 merged as part of https://github.com/openjdk/jdk/pull/15710. https://github.com/openjdk/jdk/commit/edd454b502b9bacde55492820e52655bbac63b89.patch could be cleanly applied.

Below are the test results:
* before_release: **1557.98s user 220.66s system 287% cpu 10:17.90 total**
* after_release: **1653.52s user 203.46s system 1340% cpu 2:18.54 total**
* before_fastdebug: **1045.98s user 114.93s system 182% cpu 10:35.68 total**
* after_fastdebug: **1082.15s user 111.88s system 795% cpu 2:30.11 total**

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

Commit messages:
 - Backport edd454b502b9bacde55492820e52655bbac63b89

Changes: https://git.openjdk.org/jdk17u-dev/pull/1818/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1818&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315766
  Stats: 22 lines in 1 file changed: 20 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1818.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1818/head:pull/1818

PR: https://git.openjdk.org/jdk17u-dev/pull/1818