RFR: 8273821: Limit parallelism for sanity/client/SwingSet tests

[Phil Race]

On Wed, 15 Sep 2021 14:18:09 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> If you run them today on a parallel machine with the usual invocation:
> 
> $ CONF=linux-x86_64-server-fastdebug make run-test TEST=sanity/client/SwingSet/
> 
> ...then a whole lot of these tests would fail. It seems to be caused by the overlapping GUI windows that robots fail to reach properly then. It seems these tests need to be run exclusively. 
> 
> @mrserb, maybe I am missing something? How do you run these tests? 
> 
> Additional testing:
>  - [x] `sanity/client/SwingSet/` tests now pass on TR 3970X

We run headful and headless tests in SEPARATE jtreg runs because there if you set JOBS=1 for all tests that's inefficient for the headless tests.

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PR: https://git.openjdk.java.net/jdk/pull/5533