RFR: JDK-8325139: JFR SwapSpace event - add free swap space information on Linux when running in a container environment [v8]

[Matthias Baesken]

> The JFR SwapSpace event (added by [JDK-8324287](https://bugs.openjdk.org/browse/JDK-8324287)) has been added but in a Linux containerized environment we currently just report -1, this should be enhanced. There is already some code in the mbeans (but in Java) that does something similar .

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  Adjust check in test, remove else case in memory_and_swap_usage_in_bytes

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17966/files
  - new: https://git.openjdk.org/jdk/pull/17966/files/5228f9bf..f82b9fba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17966&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17966&range=06-07

  Stats: 26 lines in 2 files changed: 18 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/17966.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17966/head:pull/17966

PR: https://git.openjdk.org/jdk/pull/17966