[11u] RFR 8267561: Shenandoah: Reference processing not properly setup for outside of cycle degenerated GC

[Zhengyu Gu]

Alibaba reported that Shenandoah outside-of-cycle degenerated GC slowly 
leak, please see CR for details.

The cause is that reference processing not setup properly during 
outside-of-cycle degenerated GC.

Webrev: http://cr.openjdk.java.net/~zgu/JDK-8267561/webrev.00/

Test:
   hotspot_gc_shenandoah
   specJVM Debery with configuration reported in CR.

Thanks,

-Zhengyu