RFR: Tests should use all heuristics and pass heap verification

[Aleksey Shipilev]

Hi,

This a long-standing issue with our in-forest tests: they should really use all
heuristics and enable heap verification. Also, we need to put the tests in
proper categories, and remove some cruft, while we are at it.

Webrev:
  http://cr.openjdk.java.net/~shade/shenandoah/tests-verify/webrev.01/

This makes hotspot_gc_shenandoah longer: 7 minutes -> 15 minutes on my desktop.
Seems like a fair trade for extended testing coverage.
hotspot_fast_gc_shenandoah still runs in under a minute.

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey