RFR: Bind WeakProcessor properly: simpler closures, asserts, parallelism

[Roman Kennke]

Looks good!

Thanks!
Roman

> http://cr.openjdk.java.net/~shade/shenandoah/weak-processor-bind/webrev.01/
> 
> This patch addresses the leftover issues in WeakProcessor handling with
> Shenandoah. It depends on bitmaps refactoring, because it uses new asserts.
> 
> Testing: tier3_gc_shenandoah (fastdebug), tier1_gc_shenandoah (release)
> 
> Thanks,
> -Aleksey
>