Merged revision(s) 1570931 from lucene/dev/trunk:
SOLR-5764: Make error message of SolrTestCaseJ4.getFile() more readable.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1570932 13f79535-47bb-0310-9956-ffa450edef68