SOLR-4952: ConvertedLegacyTest shouldn't assuming an absolute score now that we are randomizing merge policy settings, term stats may fluctuate (merge r1511044)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1511046 13f79535-47bb-0310-9956-ffa450edef68