SOLR-4602: ZkController#unregister should cancel it's election participation before asking the Overseer to delete the SolrCore information.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1457594 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4601: A Collection that is only partially created and then deleted will leave pre allocated shard information in ZooKeeper.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1457595 13f79535-47bb-0310-9956-ffa450edef68