[crac] RFR: 8347060: [CRaC] Some tests cannot run in parallel

[Timofei Pushkin]

Fixes some CRaC tests so that they can be run concurrently. This should somewhat stabilize those tests in GitHub Actions.

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Commit messages:
 - CRaC tests cannot run in parallel
 - Remove unused import

Changes: https://git.openjdk.org/crac/pull/173/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=173&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347060
  Stats: 72 lines in 4 files changed: 40 ins; 20 del; 12 mod
  Patch: https://git.openjdk.org/crac/pull/173.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/173/head:pull/173

PR: https://git.openjdk.org/crac/pull/173