RFR: Filter out heap walk related hotspot_serviceability test

[Aleksey Shipilev]

On 11/28/18 9:13 PM, Zhengyu Gu wrote:
> 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/

(sighs)

I wonder if "!vm.gc.Shenandoah" is accepted? If so, it looks cleaner.

-Aleksey