[crac] RFR: RestoreEnvironmentTest refactoring

[Roman Marchenko]

The test was extended with the example to illustrate the scenario when an user don't like to propagate some of environment variables into a restored process (see `RESTORE_ENVIRONMENT_TEST_VAR2` in `RestoreEnvironmentTest.sh`). See the initial discussion here #30

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Commit messages:
 - RestoreEnvironmentTest is extended with an example

Changes: https://git.openjdk.org/crac/pull/42/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=42&range=00
  Stats: 10 lines in 2 files changed: 5 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/crac/pull/42.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/42/head:pull/42

PR: https://git.openjdk.org/crac/pull/42