RFR: ShenandoahPushWorkerQueuesScope should subclass ShenandoahPushWorkerScope

[Roman Kennke]

Good! Go!

Thanks,
Roman


> To eliminate duplicate code for pushing worker scope.
> 
> Webrev:
> http://cr.openjdk.java.net/~zgu/shenandoah/queue_scope_cleanup/webrev.00/
> 
> Test:
> 
>   tier3_gc_shenandoah (fastdebug and release)
> 
> Thanks,
> 
> -Zhengyu