RFR: Fix ShenandoahStrDedupStress test OOM

[Aleksey Shipilev]

On 07/18/2018 04:47 PM, Zhengyu Gu wrote:
> Nightly tests showed ShenandoahStrDedupStress test OOM on static heuristics.
> 
> The solution is to reduce live data size, but increase string mutations to archive enough GC cycles.
> It increases test time slightly.
> 
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/strdedup_test_oom/webrev.00/

Looks good.

-Aleksey