[crac] RFR: 8352413: [CRaC] crexec fails to pass some options when CRAC_CRIU_OPTS is already used [v4]

[Timofei Pushkin]

> ~~This contains the change from #216 so that should be merged first.~~ UPD: rebased.
> 
> The fix itself is small but coming up with a way to test it was not trivial:
> 1. I've split `jdk/crac/CracEngineOptionsTest.java` onto `jdk/crac/engineOptions/ParsingTest.java` and `jdk/crac/engineOptions/HelpTest.java` because it was getting too large (nothing added/removed, just split).
> 2. Added `jdk/crac/engineOptions/CracCriuOptsTest.java` to regression-test the main fix of this PR (this test depends on #216).
> 3. Removed a part that tested that `args` are actually applied by `crexec` from `jdk/crac/VMOptionsTest.java` because (2) is now effectively tests this (`VMOptionsTest` wasn't a proper place for this to begin with, it just was convenient).

Timofei Pushkin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Fix comment in CracCriuOptsTest.java
 - Take variable out of loop
 - Fix CRAC_CRIU_OPTS appending

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

Changes:
  - all: https://git.openjdk.org/crac/pull/217/files
  - new: https://git.openjdk.org/crac/pull/217/files/10d11b70..4c8cc2bd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=217&range=03
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=217&range=02-03

  Stats: 14292 lines in 2543 files changed: 7637 ins; 2326 del; 4329 mod
  Patch: https://git.openjdk.org/crac/pull/217.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/217/head:pull/217

PR: https://git.openjdk.org/crac/pull/217