SOLR-5325: ZooKeeper connection loss can cause the Overseer to stop processing commands.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_5@1531325 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5325: raise retry padding a bit

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_5@1531327 13f79535-47bb-0310-9956-ffa450edef68