[jdk17u] RFR: 8272783: Epsilon: Refactor tests to improve performance

[Aleksey Shipilev]

On Wed, 8 Sep 2021 15:54:57 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Clean backport to improve testing.
> 
> Additional testing:
>  - [x] `gc/epsilon` pass faster

Got the push approval.

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PR: https://git.openjdk.java.net/jdk17u/pull/56