[jdk8u-dev] RFR: 8301332: [8u] Fix writing of test files after the cgroups v2 backport

[Severin Gehwolf]

Please review this trivial refactoring of test files. It fixes usages of `Files.write(..., String.getBytes())`  to `Files.write(..., String.getBytes(StandardCharsets.UTF-8))`. Affected files don't contain non-ascii content, but it's a good cleanup to do anyway.

Testing:
- [x] Tests compile, run and pass (as before)

Thoughts?

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

Depends on: https://git.openjdk.org/jdk8u-dev/pull/218

Commit messages:
 - 8301332: [8u] Fix writing of test files after the cgroups v2 backport

Changes: https://git.openjdk.org/jdk8u-dev/pull/252/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=252&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301332
  Stats: 50 lines in 3 files changed: 0 ins; 0 del; 50 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/252.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/252/head:pull/252

PR: https://git.openjdk.org/jdk8u-dev/pull/252