SOLR-6108: Add support for 'addreplica' Collection API in SolrJ

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1596820 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6104: The 'addreplica' Collection API does not support 'async' parameter

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1596823 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6101: Shard splitting doesn't work when legacyCloud=false is set in cluster properties

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1596830 13f79535-47bb-0310-9956-ffa450edef68