RFR: 8203359: Container level resources events

[Jaroslav Bachorik]

With this change it becomes possible to surface various cgroup level metrics (available via `jdk.internal.platform.Metrics`) as JFR events.

Only a subset of the metrics exposed by `jdk.internal.platform.Metrics` is turned into JFR events to start with.
* CPU related metrics
* Memory related metrics
* I/O related metrics

For each of those subsystems a configuration data will be emitted as well. The initial proposal is to emit the configuration data events at least once per chunk and the metrics values at 30 seconds interval. 
By using these values the emitted events seem to contain useful information without increasing overhead (the metrics values are read from `/proc` filesystem so that should not be done too frequently).

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

Commit messages:
 - Formatting spaces
 - 8203359: Container level resources events

Changes: https://git.openjdk.java.net/jdk/pull/3126/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3126&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8203359
  Stats: 389 lines in 8 files changed: 386 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3126.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3126/head:pull/3126

PR: https://git.openjdk.java.net/jdk/pull/3126