hg: shenandoah/jdk: Cherry-pick: 8221688: Quarantine Shenandoah string dedup tests

[zgu at redhat.com]

Changeset: 223096d4a9ad
Author:    zgu
Date:      2019-03-29 10:21 -0400
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/223096d4a9ad

Cherry-pick: 8221688: Quarantine Shenandoah string dedup tests
Reviewed-by: rkennke

! test/hotspot/jtreg/ProblemList.txt