[jdk8u-dev] RFR: 8239785: Cgroups: Incorrect detection logic on old systems in hotspot [v8]

[Jonathan Dowland]

> This is a backport of add18914fb1294999877b563c734a25b4c17b922 for cgroups v2 support injdk8u-dev, via the 11u backport.
> 
> It does not apply clean:
> 
>  * context issues for changes made for the different approach for logging in 8u
>  * copyright lines
> 
> Small amount of re-working of new code that used `log_trace`/`log_debug` to use the 8u approach.

Jonathan Dowland 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:

 - Update file path in comment
 - Severin's test fixes. Thanks!
 - Move test to a more 8u-appropriate location
   
   Container (cgroups, docker) tests in 8u reside in
   hotspot/test/runtime/containers
 - remove duplicate include of osContainer_linux
   
   With the backport of 8189762, the include of osContainer_linux was
   moved to a later #ifdef stanza, relative to the original. This caused
   a context problem with this backport.
 - 8239785: Cgroups: Incorrect detection logic on old systems in hotspot
   
   Return NULL subsystem if no cgroup controllers are mounted.
   
   Reviewed-by: sgehwolf
   Backport-of: add18914fb1294999877b563c734a25b4c17b922

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

Changes:
  - all: https://git.openjdk.org/jdk8u-dev/pull/135/files
  - new: https://git.openjdk.org/jdk8u-dev/pull/135/files/5bc91b88..2de43617

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=135&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=135&range=06-07

  Stats: 47 lines in 3 files changed: 42 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/135.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/135/head:pull/135

PR: https://git.openjdk.org/jdk8u-dev/pull/135