RFR: 8253750: use build-stable default seed for Utils.RANDOM_GENERATOR [v3]

[Igor Ignatyev]

On Mon, 5 Oct 2020 21:04:52 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Can you take a look at the existing jdk.test.lib.RandomFactory and see if we can avoid a separate random number
> generator and property?

I am not adding a new separate random number generator or a new property, `jdk.test.lib.Utils.getRandomInstance` has
been around for a long time and is used by lots of tests (most of them are in `/test/hotspot/jtreg`). merging
`Utils.getRandomInstance` and `RandomFactory` (or rather replacing one w/ another) is tracked by
[JDK-8212077](https://bugs.openjdk.java.net/browse/JDK-8212077).

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