[jdk11u-dev] RFR: 8239785: Cgroups: Incorrect detection logic on old systems in hotspot

[Jonathan Dowland]

This is a backport of 8239785 for jdk11u. The dependent backports have now all been integrated.

This PR replaces #881 which was stuck with a dependency on a superseded dependent PR.

It's not clean, but the only conflict was the copyright line in the
comment header for src/hotspot/share/prims/whitebox.hpp.

I'm checking jtreg tests in test/hotspot/jtreg/containers on a mixture of cgroup v1 and v2 systems now.

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### Progress
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Commit messages:
 - 8239785: Cgroups: Incorrect detection logic on old systems in hotspot

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/946/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=946&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8239785
  Stats: 695 lines in 6 files changed: 526 ins; 96 del; 73 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/946.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/946/head:pull/946

PR: https://git.openjdk.java.net/jdk11u-dev/pull/946