RFR: JDK-8325139: JFR SwapSpace event - add free swap space information on Linux when running in a container environment [v7]

[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 two additional commits since the last revision:

 - remove empty line is os_linux
 - adjust os::free_swap_space Linux

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17966/files
  - new: https://git.openjdk.org/jdk/pull/17966/files/3af01267..5228f9bf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17966&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17966&range=05-06

  Stats: 21 lines in 1 file changed: 11 ins; 6 del; 4 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