SOLR-6592: Avoid waiting for the leader to see the down state if that leader is not live.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1631442 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6511: fix back compat issue when reading existing data from ZK

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1631444 13f79535-47bb-0310-9956-ffa450edef68