[8u] RFR: 8226575: OperatingSystemMXBean should be made container aware

[Severin Gehwolf]

Hi,

Please review this OpenJDK 8u backport for OperatingSystemMXBean's
container awareness which has been backported to Oracle JDK (parity
bug). This backport depends on JDK-8203357[1] for Metrics.java which is
being used in this patch.

Changes as compared to the JDK 11 patch were:

 * SubSystem.java: 8217338: [Containers] Improve systemd slice memory
   limit support not being there => getLongValueMatchingLine() missing
   => dropped
 * OperatingSystemImpl.java: Introduced Java methods which internally
   call the native methods. Renamed native methods to <oldmethod-name>0
 * Tests were actually done to the hotspot code in later JDKs, thus,
   for this backport the tests are in the hotspot portion of the webrev
   (separate repo).
 * Other than that, it's just the native bits which are in different
   files in JDK 8.

Bug: https://bugs.openjdk.java.net/browse/JDK-8226575
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8226575/jdk8/01/
CSR: https://bugs.openjdk.java.net/browse/JDK-8248804

Testing: Included docker tests on Linux x86_64. jdk_management tests and
tier 1 tests. No regressions noted.

If somebody could test this on Windows/Mac, I'd appreciate it.

Thanks,
Severin

[1] http://mail.openjdk.java.net/pipermail/jdk8u-dev/2020-July/012164.html