RFR: Adaptive CSet selection overshoots max-CSet

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/adaptive-cset-overshoot/webrev.01/

The comment says "When max_cset is hit, we terminate the cset selection", which is exactly what we
want to avoid trying to evacuate more data than available free space. Unfortunately, current code
allows overshooting it, when we are going via (new_garbage < min_garbage) line. Makes LRUFragger run
out of memory.

Testing: tier3_gc_shenandoah, specjbb, LRUFragger

Thanks,
-Aleksey