SOLR-6402: Only exit the thread loop on a KeeperException if it's expiration.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619794 13f79535-47bb-0310-9956-ffa450edef68
 SOLR-5244: Exporting Full Sorted Result Sets

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619804 13f79535-47bb-0310-9956-ffa450edef68