RFR: 8340092: [Linux] containers/systemd/SystemdMemoryAwarenessTest.java failing on some systems [v3]

[Severin Gehwolf]

> Please review this trivial test fix. The test fails if the `<slice>.d` directory already exists (for some reason). It needs to exist for the test to work. But if it exists we ignore the failure, thus using `Files.createDirectories()`.
> 
> As a benefit I've also added `exclusiveAccess.dirs=.` to the `systemd` test directory to match container tests in `docker` folder and added `TRUNCATE_EXISTING` and `CREATE` open options for files in the `<slice>.d` directory. Both of which should ensure the test runs more reliably.
> 
> Testing:
> - [x] GHA
> - [x] Manual testing by creating the directory first, running the test. Failed. The same handshake passes after the patch. Similarly for the user manager service not being accessible (for some reason).
> 
> Thanks!

Severin Gehwolf 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 five additional commits since the last revision:

 - Merge branch 'master' into jdk-8340092-test-fix
 - Cleanup files when systemd --user fails
 - Skip test if systemd user manager not properly working
 - Add CREATE open option.
 - 8340092: [Linux] containers/systemd/SystemdMemoryAwarenessTest.java failing on some systems

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20989/files
  - new: https://git.openjdk.org/jdk/pull/20989/files/4fde8dfd..e88613df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20989&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20989&range=01-02

  Stats: 4510 lines in 101 files changed: 2945 ins; 980 del; 585 mod
  Patch: https://git.openjdk.org/jdk/pull/20989.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20989/head:pull/20989

PR: https://git.openjdk.org/jdk/pull/20989