RFR: 8300659: Refactor TestMemoryAwareness to use WhiteBox api for host values

[Severin Gehwolf]

Please review this refactoring of a container test. It now uses WhiteBox to retrieve the host values it asserts for. In terms of functionality this is basically a no-op except for the now more precise assertion on systems with swap accounting disabled at the kernel level.

*Testing*
- [x] Container tests on Linux x86_64 cgv1 and cgv2
- [x] Container tests on Linux x86_64 cgv1 and cgv2 on systems with swapaccount=0
- [ ] GHA in progress 

Thoughts?

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Commit messages:
 - 8300659: Refactor TestMemoryAwareness to use WhiteBox api for host values

Changes: https://git.openjdk.org/jdk/pull/12097/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12097&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300659
  Stats: 44 lines in 3 files changed: 27 ins; 1 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/12097.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12097/head:pull/12097

PR: https://git.openjdk.org/jdk/pull/12097