RFR: 8317347: Parallel: Make TestInitialTenuringThreshold use createTestJvm

[Leo Korinth]

Also add parallel flag for first invocation (this is a bug). Initial testing ok, but will run tiers before pushing.

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

Commit messages:
 - 8317347: Parallel: Make TestInitialTenuringThreshold use createTestJvm

Changes: https://git.openjdk.org/jdk/pull/16009/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16009&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/jdk/pull/16009.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16009/head:pull/16009

PR: https://git.openjdk.org/jdk/pull/16009