RFR: 8253714: [cgroups v2] Soft memory limit incorrectly using memory.high

[Severin Gehwolf]

Tests using `--memory-reservation` started to fail with newer `crun` cgroups v2-capable runtime. It turns out it was
incorrectly setting `memory.high` in an early version and got fixed to set `memory.low` now instead. This change
accounts for that.

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

Commit messages:
 - 8253714: [cgroups v2] Soft memory limit incorrectly using memory.high

Changes: https://git.openjdk.java.net/jdk/pull/381/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=381&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253714
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/381.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/381/head:pull/381

PR: https://git.openjdk.java.net/jdk/pull/381