[14] RFR(XS) 8235776: Shenandoah: Shenandoah root updater not always uses right code blob closure

[Zhengyu Gu]

Please review this small patch that updates/disarms nmethods during root 
updating if concurrent class unloading is enabled.


Bug: https://bugs.openjdk.java.net/browse/JDK-8235776
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8235776/webrev.00/


Test:
   hotspot_gc_shenandoah (fastdebug and release)

Thanks,

-Zhengyu