RFR: Filter out heap walk related hotspot_serviceability test

[Zhengyu Gu]

After disabling heap walk, these two tests started to fail. There might 
be more under vmTestbase, will check next.

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

Thanks,

-Zhengyu