[jdk8u-dev] RFR: 8253939: [TESTBUG] Increase coverage of the cgroups detection code [v2]

[Jonathan Dowland]

> This is a backport of 8253939  to jdk8u-dev for cgroups v2 support.
> 
> It's not clean: several `Files.writeString` → `Files.write(…,.getBytes())` changes needed.

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 74 additional commits since the last revision:

 - 8253939: [TESTBUG] Increase coverage of the cgroups detection code
   
   Backport-of: 42fc15899115ca61151bbee96b5580d4e4252beb
 - replace use of Optional.isEmpty
 - 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible)
   
   Backport-of: 2bbf8a2a964a64d88298a3dd184459af506e58ed
 - Severin's test fixes. Thanks!
 - Replace log_warning with tty->print_cr
 - 8253435: Cgroup: 'stomping of _mount_path' crash if manually mounted cpusets exist
   
   Backport-of: 0054c15f60cce6470be05d29bfacbdb74cfb7bc9
 - 8252359: HotSpot Not Identifying it is Running in a Container
   
   Backport-of: 76f0588aaf265439a589cceb924e3ea9d3fda8f1
 - replace log_trace with tty->print_cr
 - 8278951: containers/cgroup/PlainRead.java fails on Ubuntu 21.10
   
   Reviewed-by: sgehwolf
   Backport-of: 35172cdaf38d83cd3ed57a5436bf985dde2d802b
 - PlainRead: ProcessBuilder: jdk8u-appropriate command line flags
 - ... and 64 more: https://git.openjdk.org/jdk8u-dev/compare/3640d59a...72765b59

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

Changes:
  - all: https://git.openjdk.org/jdk8u-dev/pull/169/files
  - new: https://git.openjdk.org/jdk8u-dev/pull/169/files/3640d59a..72765b59

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=169&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=169&range=00-01

  Stats: 4480 lines in 127 files changed: 3197 ins; 781 del; 502 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/169.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/169/head:pull/169

PR: https://git.openjdk.org/jdk8u-dev/pull/169