[crac] RFR: 8364538: [CRaC] Test CRaCIgnoreRestoreIfUnavailable

[Timofei Pushkin]

Adds tests for `CRaCIgnoreRestoreIfUnavailable`.

The case for incompatible CPU features is not tested, although I believe it should work. Such test would be more complex (to the best of my knowledge, emulation is needed to be able to reduce the set of available features between checkpoint and restore) so it deserves a separate task. It would be something like what `test/jdk/jdk/crac/CPUFeatures/CPUFeatures.sh` does (have never run it, not sure if it works).

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Commit messages:
 - Remove old comment
 - Fix years in license headers
 - Test CRaCIgnoreRestoreIfUnavailable

Changes: https://git.openjdk.org/crac/pull/255/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=255&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364538
  Stats: 294 lines in 5 files changed: 289 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/crac/pull/255.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/255/head:pull/255

PR: https://git.openjdk.org/crac/pull/255