OAK-925 - Query: Lucene index loads all path in memory

Modified the LucenePathCursor to use an iterator for fetching LuceneResultRow. The iterator impl would fetch lucene results in batches of 50

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1587504 13f79535-47bb-0310-9956-ffa450edef68