RFR (S): Matrix verification leaks reserved memory

[Aleksey Shipilev]

Hi,

Some overnight runs crashed with failure to reserve memory. That's because we
leak reserved memory in verification code. The apparent solution is just to
reserve/commit the memory once during ShenandoahHeap initialization when
verification is enabled:
  http://cr.openjdk.java.net/~shade/shenandoah/matrix-verify-leak/webrev.01/

Testing: hotspot_gc_shenandoah, failing tests

Thanks,
-Aleksey