hg: shenandoah/jdk: Rearrange Shenandoah tests into 3 tiers

[zgu at redhat.com]

Changeset: 9d6504c6933c
Author:    zgu
Date:      2018-06-01 15:18 -0400
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/9d6504c6933c

Rearrange Shenandoah tests into 3 tiers

! test/hotspot/jtreg/TEST.groups