[jdk8u-dev] RFR: 8284977: MetricsTesterCgroupV2.getLongValueEntryFromFile fails when named value doesn't exist

[kurashige]

Hi all,

I'd like to backport this to jdk8u-dev.
It fixes a test failure caused by cgroups virtual files (nr_periods etc) not existing in some circumstances.

Thanks.

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Commit messages:
 - Backport 444a0d98ac06ab043e3b11281234fd515abff302

Changes: https://git.openjdk.org/jdk8u-dev/pull/215/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=215&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8284977
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/215.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/215/head:pull/215

PR: https://git.openjdk.org/jdk8u-dev/pull/215