[15] RFR 8246458: Shenandoah: TestAllocObjects.java test fail with -XX:+ShenandoahVerify

[Zhengyu Gu]

We should not run root verifier if OOM during evacuating/updating roots 
in final mark phase, cause there is no guarantee that they are consistent.

Bug: https://bugs.openjdk.java.net/browse/JDK-8246458
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8246458/weberv.00/

Test:
   hotspot_gc_shenandoah


Thanks,

-Zhengyu