RFR: Fix ShenandoahHeapRegion initialization

[Aleksey Shipilev]

On 02/01/2017 04:47 PM, Roman Kennke wrote:
> Aleksey found out that ShenandoahHeapRegion::_critical_pins is never
> initialized. I had a look and there are also some other fields in
> ShenandoahHeapRegion uninitialized... we seem to be lucky that the OS
> zeroes memory for us, and no other allocations interfered with us.
> Don't like to rely on luck though, so here's the fix:
> 
> http://cr.openjdk.java.net/~rkennke/fixhr/webrev.00/

Should probably start with _recycled(true) to match whatever recycle() is doing.
Otherwise looks good.

Thanks,
-Aleksey