RFR: JDK-8266490: Extend the OSContainer API to support the pids controller of cgroups [v5]

[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
>   }

Matthias Baesken has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into JDK-8266490
 - Add hotspot tests
 - test and small adjustments suggested by Severin
 - Adjustments following Severins comments
 - JDK-8266490

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4518/files
  - new: https://git.openjdk.java.net/jdk/pull/4518/files/3fe73c3c..5fc52fb1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4518&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4518&range=03-04

  Stats: 675520 lines in 5968 files changed: 547978 ins; 105328 del; 22214 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