SOLR-6157: re-enable this test to see if it runs consistently on Jenkins (beast passed 20/20)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1630140 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6513: Add a collectionsAPI call BALANCESLICEUNIQUE

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1630143 13f79535-47bb-0310-9956-ffa450edef68