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

[Roger Riggs]

On Fri, 2 Oct 2020 20:46:48 GMT, Igor Ignatyev <iignatyev at openjdk.org> wrote:

>> Hi all,
>> 
>> could you please review the patch which updates `jdk.test.lib.Utils` to use md5 hash-sum of `java.vm.version` property
>> as default seed for `Utils.RANDOM_GENERATOR`?
>> from JBS:
>>> using the same seed for all runs of a build will make it possible (easier) to compare results from different test runs
>>> (e.g. on different platforms, w/ different flags) and consequently will make test results analysis easier. the proposed
>>> solution is to use the seed based on Runtime.version() / "java.vm.version", which are different from build to build, if
>>> there is no seed specified by "jdk.test.lib.random.seed" property.
>> 
>> the patch also updates `RandomGeneratorTest` test, so it expects now that the same values are generated if no seed is
>> provided.
>> testing: ✅ tier1
>
> 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

The code and description are reversed from what I suggested.

The seed should *only* be computed from the version information if it is a promoted or weekly build.
All other builds should use a random seed.

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Changes requested by rriggs (Reviewer).

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