RFR: Move Shenandoah stress tests to tier3

[Roman Kennke]

Am 27.07.2018 um 16:37 schrieb Zhengyu Gu:
> Currently, our stress tests are in tier2. The six stress tests take more
> to run than the rest of 82 tests, which makes little difference, in term
> of testing time, between tier2 and tier3.
> 
> By moving stress tests to tier3, tier2 takes about 20 minutes to run on
> my local machine (vs. about 1 hour), which is more reasonable testing
> time for trivial changes.
> 
> 
> Wberev: http://cr.openjdk.java.net/~zgu/shenandoah/sh-test-tiers/webrev.00/
> 

It sounds reasonable and patch looks good to me.

Roman