SOLR-5587: ElectionContext implementations should use ZkCmdExecutor#ensureExists to ensure their election paths are properly created.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1554116 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4709: The core reload after replication if config files have changed can fail due to a race condition. 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1554118 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5503: Retry 'forward to leader' requests less aggressively - rather than on IOException, ConnectException.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_6@1554122 13f79535-47bb-0310-9956-ffa450edef68