RFR: JDK-8266490: Extend the OSContainer API to support the pids controller of cgroups

[Matthias Baesken]

Hello, please review this PR; it extend the OSContainer API in order to also support the pids controller of cgroups.

I noticed that unlike the other controllers "cpu", "cpuset", "cpuacct", "memory"  on some older Linux distros (SLES 12.1, RHEL 7.1) the pids controller might not be there (or not fully supported) so it was added as optional  , see the coding


  if (!cg_infos[PIDS_IDX]._data_complete) {
    log_debug(os, container)("Optional cgroup v1 pids subsystem not found");
    // keep the other controller info, pids is optional
  }

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Commit messages:
 - JDK-8266490

Changes: https://git.openjdk.java.net/jdk/pull/4518/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4518&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266490
  Stats: 203 lines in 16 files changed: 159 ins; 2 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4518.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4518/head:pull/4518

PR: https://git.openjdk.java.net/jdk/pull/4518