[crac] RFR: Support extra criu flags from the environment [v2]

[Anton Kozlov]

On Thu, 30 Jun 2022 17:12:02 GMT, Volker Simonis <simonis at openjdk.org> wrote:

>> When testing with different `criu` versions or `criu` configurations it might be useful to be able to modify the default  `criu` command line parameters. This PR introduces the new environment variable `CRAC_CRIU_OPTS` which will be interpreted as a space separated list of `criu` flags to be appended to the hard-coded list of command line parameters. E.g.
>> 
>> 
>> $ CRAC_CRIU_OPTS="-v4 -o resume.log -W /tmp/crac" java -XX:CRaCRestoreFrom=/tmp/crac
>> 
>> 
>> This will set the logging level to 4 (thus overriding the hard-coded logging level of 1 for resuming), redirect the log to the file `resume.log` and change `criu`'s working directory (which will contain the log file) to `/tmp/crac`.
>
> Volker Simonis has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Drop surplus arguments from CRAC_CRIU_OPTS and issue a warning

Looks good to me. Thanks!

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

Marked as reviewed by akozlov (Lead).

PR: https://git.openjdk.org/crac/pull/26