[jdk21u] RFR: 8315442: Enable parallelism in vmTestbase/nsk/monitoring/stress/thread tests

[Aleksey Shipilev]

Clean backport to improve testing times. The change was in mainline for about 7 weeks, without bugtail.

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

Commit messages:
 - Backport 9013b032448518e09a7c6f2e80054be722c970a3

Changes: https://git.openjdk.org/jdk21u/pull/298/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=298&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315442
  Stats: 483 lines in 21 files changed: 0 ins; 483 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u/pull/298.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/298/head:pull/298

PR: https://git.openjdk.org/jdk21u/pull/298