RFR: 8253750: use build-stable default seed for Utils.RANDOM_GENERATOR [v2]

[Igor Ignatyev]

On Fri, 2 Oct 2020 18:46:39 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Igor Ignatyev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   used Runtime.version() instead of ${java.vm.version}
>>   updated javadoc
>
> ok, if I read the code closely and know how the promoted build process works then I see your rationale.
> Please update the bug report and edit the PR description to describe the conditions under which the seed
> for random is computed from the build number. Its might be clearer to refer to the Runtime.Version build information
> in the description.  Also make it clear that unless the system property is set, it will use a 'random' seed.

@RogerRiggs , I have updated the code to use `Runtime::version` and updated the docs to better reflect how `seed` value
is being set, as well as added some explanation to both the JBS issue and PR. please let me know if it's still not
clear enough.

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PR: https://git.openjdk.java.net/jdk/pull/391