OAK-2235 - Lucene index not created if no node is indexed

By default IndexWriter is lazily created but if logic detects its a reindex mode then it would initialize write and that would create an empty index dir

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1634864 13f79535-47bb-0310-9956-ffa450edef68