RFR (L) 8227327: Shenandoah: Faster and more parallel tests

[Roman Kennke]

Very nice! Patch looks good!

Roman

> Current hotspot_gc_shenandoah suite runs in fastdebug like this:
> 
> real	31m31.172s
> user	287m50.380s
> sys	5m28.277s
> 
> This amounts to 9.1x parallelism on 16-thread machine. Clearly, something big is on the critical
> path. Profiling shows the critical path is largely dominated by GCBasherWithShenandoah, which takes
> 26 minutes to run through all configurations. Other huge tests also run for a long time.
> 
> We can improve this by splitting @run into several @test groups -- this would execute @test-s in
> parallel, reducing the impact on critical path. The convenient way to split is by mode: passive,
> normal, traversal.
> 
> Also, we can remove some the useless configurations from the tests. This becomes apparent once we
> reformat @run sections to be more digestible and following the same format.
> 
> Webrev:
>   https://cr.openjdk.java.net/~shade/8227327/webrev.01/
> 
> Patched version runs like this:
> 
> real	17m53.136s
> user	247m50.750s
> sys	5m33.051s
> 
> So, it yields ~13.7x parallelism on 16-thread machine, and does less work.
> 
> Testing: hotspot_gc_shenandoah (d'uh)
>