SOLR-3852: Fixed ZookeeperInfoServlet so that the SolrCloud Admin UI pages will work even if ZK contains nodes with data which are not utf8 text (merge r1519763)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1519779 13f79535-47bb-0310-9956-ffa450edef68