RFR: Unclutter ShenandoahHeap, take 2

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/unclutter-sh-heap-2/webrev.01/

Since recent sh/jdk merge wrecked up my patch that reorders stuff in shenandoahHeap.hpp, I prefer to
push the parts of pending shenandoahHeap.cpp changes ahead. This would give me the opportunity to
just copy over the "new" shenandoahHeap.hpp with reshuffling over the old one.

Testing: tier3_gc_shenandoah

Thanks,
-Aleksey