cleanup TestSolrCoreProperties so that it's less hackish and absurd -- and while we're at it, close the book on SOLR-4952 (merge r1513996)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1514001 13f79535-47bb-0310-9956-ffa450edef68