RFR: 8374364: TestCgroupMetrics.java fails when docker service unavailable

[SendaoYan]

Hi all,

Test jdk/internal/platform/cgroup/TestCgroupMetrics.java report fails when the docker service is unavailable. The details shows in jbs issue. I think it's better to call `DockerTestUtils.checkCanTestDocker()` before run this test.

Change has been verified locally. Test-fix only, no risk.

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Commit messages:
 - 8374364: TestCgroupMetrics.java fails when docker service unavailable

Changes: https://git.openjdk.org/jdk/pull/28996/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28996&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374364
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28996.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28996/head:pull/28996

PR: https://git.openjdk.org/jdk/pull/28996