RFR (S) 8247751: Shenandoah: options tests should run with smaller heaps

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8247751

On huge machines, the default heap sizes are quite large, and memory zapping takes quite some time
to startup in fastdebug mode. We should be running at least "options" tests with smaller default heaps.

Fix:
  https://cr.openjdk.java.net/~shade/8247751/webrev.01/

Testing: hotspot_gc_shenandoah (faster now)

-- 
Thanks,
-Aleksey