[jdk21u] RFR: 8315437: Enable parallelism in vmTestbase/nsk/monitoring/stress/classload tests

[Aleksey Shipilev]

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

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Commit messages:
 - Backport dd214d0f9543f125ef514eb3a60a65a5f514b1ca

Changes: https://git.openjdk.org/jdk21u/pull/297/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=297&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315437
  Stats: 552 lines in 24 files changed: 0 ins; 552 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u/pull/297.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/297/head:pull/297

PR: https://git.openjdk.org/jdk21u/pull/297