RFR: 8334254: Cleanup CGroups initialization code [v2]

[Johan Sjölen]

> Hi,
> 
> Please consider this patch which attempts to improve the code quality of some of the cgroups code, somewhat.
> 
> 1. Get rid of `#define`s and upgrade to a `CG_INFO` enum, with some helpers
> 2. Make some of the code prettier by removing copy-pasted and edited code
> 3. Make `CgroupInfo` RAII, ridding us of the `cleanup` function
> 4. `set_subsystem_path` is **only** used at construction time, only call it at that time and make those functions private. Also remove `virtual`ness, as this is unnecessary now.
> 
> Testing:
> 
> 1. cgroupTest group in gtest.
> 
> Thank you.

Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:

  Review comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19709/files
  - new: https://git.openjdk.org/jdk/pull/19709/files/6f65ffc6..10ab97ff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19709&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19709&range=00-01

  Stats: 6 lines in 3 files changed: 3 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19709.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19709/head:pull/19709

PR: https://git.openjdk.org/jdk/pull/19709