LUCENE-6105: don't cache root arcs for small FSTs

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1644473 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6787 removing the dependency on zk jar for post.jar 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1644489 13f79535-47bb-0310-9956-ffa450edef68