[8u] RFR: 8203357: Container Metrics

[Severin Gehwolf]

Hi,

Please review this OpenJDK 8u backport of the Java Metrics classes
which are in later JDKs. It is a pre-requisite for JDK-8226575 an
Oracle JDK parity issue. Implementations of the interface are provided
for Linux only and, thus, are compiled for Linux only. This backport
differs from the original JDK 11 change in the following way:

 * MetricsTester: Arrays.compare() => Arrays.equals(). Arrays.compare()
   is JDK 9+ only.
 * JDK-8223147: JFR Backport, brought in test library code included in
   the JDK 11 changeset. I've only done the needed adjustments to the
   relevant files in the test libary. Many were already present.
 * For this backport I've not included changes to the Launcher to
   support -XshowSettings:system (as in later JDKs).

Bug: https://bugs.openjdk.java.net/browse/JDK-8203357
webrev: 
http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8203357/jdk8/01/webrev/

Testing: Included docker tests on Linux x86_64. All pass. Though, they
are in dire need of reliability improvements which I'll work on as a
follow-up.

Thanks,
Severin