RFR: Fix number of threads used for initial evacuation

[Aleksey Shipilev]

On 02/13/2017 12:35 PM, Roman Kennke wrote:
> in ShenandoahHeap::evacuate_and_update_roots() we're using
> _max_parallel_workers to initialize the roots processor (and thus the
> StrongRootsScope), but we're not updating the workers to that (afaict).
> This patch makes the root processor use the currently active number of
> workers (should be the same as final-mark workers set earlier during
> that pause). Ok?
> 
> http://cr.openjdk.java.net/~rkennke/init-evac-workers/webrev.00/

Sounds reasonable. OK.

-Aleksey