[jdk8u-dev] RFR: 8293472: Incorrect container resource limit detection if manual cgroup fs mounts present

[Jonathan Dowland]

This is a backport of 8293472 to 8u for cgroups v2 support. Not clean: log_debug→tty->print_cr and Files.writeString → Files.write() needed, as well as adjustments for the lack of [8266490](https://bugs.openjdk.org/browse/JDK-8266490) (PID controller support) in 8u.

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Commit messages:
 - Files.writeString → Files.write() for jdk8u
 - rework two uses of log_debug
 - 8293472: Incorrect container resource limit detection if manual cgroup fs mounts present

Changes: https://git.openjdk.org/jdk8u-dev/pull/216/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=216&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293472
  Stats: 167 lines in 6 files changed: 112 ins; 29 del; 26 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/216.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/216/head:pull/216

PR: https://git.openjdk.org/jdk8u-dev/pull/216