[8u] RFR: 8217338: [Containers] Improve systemd slice memory limit support

[Severin Gehwolf]

Hi,

Please review this OpenJDK 8u port of JDK-8217338, which is a) an
Oracle JDK parity patch, b) a dependency of further container detection
backports like JDK-8232207 and JDK-8227006. The JDK 11 patch does not
apply cleanly. Changes I've done:

 * Split of the patch for hotspot and jdk repositories. JDK 11u is a
   unified repo.
 * JDK 11u has UL, which is being translated to PrintContainerInfo
   diagnostic flag in 8u.
 * Some differences in context with respect to import statements in
   Java code for Metrics

Otherwise the patch is the same. We've had this patch JDK 11 since
11.0.7 and hasn't caused any problems as far as I'm aware. As mentioned
previously, it makes getting further fixes (JDK-8232207, JDK-8227006)
easier and less risky. Therefore, I'd like to get it included for
8u282. The risk for this backport should be acceptable given the
circumstances. With that said, it's Linux-only.

Bug: https://bugs.openjdk.java.net/browse/JDK-8217338
webrev: https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8217338/jdk8/01/

Testing: Container tests on Linux x86_64 (cgroup v1). Manual test[1].

Thoughts?

Thanks,
Severin

[1] https://bugs.openjdk.java.net/browse/JDK-8217338?focusedCommentId=14378230&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14378230