[jdk21u-dev] RFR: 8317347: Parallel: Make TestInitialTenuringThreshold use createTestJvm

[Goetz Lindenmaier]

I backport this to keep the 21u test suite up-to-date. This will simplify future test backports.

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Commit messages:
 - Backport 6ee6171e8124ae8ce4f60c2582c2fe2cae6fc3db

Changes: https://git.openjdk.org/jdk21u-dev/pull/52/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=52&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317347
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/52.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/52/head:pull/52

PR: https://git.openjdk.org/jdk21u-dev/pull/52