LUCENE-4396: add test case

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1617285 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6362: fix test bug

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1617294 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6304 JsonLoader should be able to flatten an input JSON to multiple docs

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1617296 13f79535-47bb-0310-9956-ffa450edef68