SOLR-5010: single field handling

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1502247 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4914: Factor out core discovery and persistence logic

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1502276 13f79535-47bb-0310-9956-ffa450edef68