[crac] RFR: 8347430: [CRaC] ContainerPidAdjustmentTest fails on WSL

[Timofei Pushkin]

Makes `jdk/crac/ContainerPidAdjustmentTest.java` read `/proc/sys/kernel/pid_max` instead of assuming it to always be 4194304

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Commit messages:
 - ContainerPidAdjustmentTest fails on WSL

Changes: https://git.openjdk.org/crac/pull/179/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=179&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347430
  Stats: 15 lines in 1 file changed: 11 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/crac/pull/179.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/179/head:pull/179

PR: https://git.openjdk.org/crac/pull/179