[crac] RFR: Environment vars propagation into restored process [v2]

[Roman Marchenko]

> This PR provides functionality to propagate actual environment variables to a restored process, as well as the test for this functionality.
> 
> Env propagation is done in few steps:
> - Store the actual environment before restoring
> - After restoring, replace the restored `environ` with a new one.
> - On `afterRestore` event, propagate the new environment into a restored process via `ProcessEnvironment`.

Roman Marchenko has updated the pull request incrementally with one additional commit since the last revision:

  Update src/hotspot/os/linux/os_linux.cpp
  
  Fixing review comments
  
  Co-authored-by: Anton Kozlov <drakon.mega at gmail.com>

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

Changes:
  - all: https://git.openjdk.org/crac/pull/30/files
  - new: https://git.openjdk.org/crac/pull/30/files/0270dc4b..8eb394e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=30&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=30&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/crac/pull/30.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/30/head:pull/30

PR: https://git.openjdk.org/crac/pull/30