RFR[8u]: Fix force termination detection by spin master

[Zhengyu Gu]

Aleksey discovered JVM hung during backporting recent Shenandoah OWST 
terminator fix to correct force termination logic. Apparently, our 8u 
port is broken all alone, missing force termination detection by spin 
master.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/8u_force_termination/webrev.00/

Test:

   hotspot_tier3_gc_shenandoah (fastdebug and release)

Thanks,

-Zhengyu