RFR: JDK-8227039: Shenandoah: Aggressive heuristics for Traversal mode

[Roman Kennke]

 We have aggressive heuristic in normal/default mode which is great for
testing by running GC continuosly and using large/maximum collection
set. We should add similar heuristics for Traversal mode in order to
ramp up testing of it.

The traversal-aggressive heuristic mimics the normal-aggressive: it runs
GCs back-to-back and selects any region with garbage into the cset.

I added traversal-aggressive test configs whereever normal-aggressive
test configs are present.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8227039
Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8227039/webrev.00/
Testing: hotspot_gc_shenandoah

Can I please get reviews?

Thanks,
Roman