SOLR-2927: Solr does not unregister all mbeans upon exception in constructor causing memory leaks

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_10@1642728 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6685: ConcurrentModificationException in Overseer Status API

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_10@1642729 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6706: /update/json/docs throws RuntimeException if a nested structure contains a non-leaf float field

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_10@1642730 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6610: Slow startup of new clusters because ZkController.publishAndWaitForDownStates always times out

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_10@1642732 13f79535-47bb-0310-9956-ffa450edef68