SOLR-6801 Load RequestHandler from blob store

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1647539 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6883: CLUSTERPROP API switch case does not call break

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1647552 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6882: Misspelled collection API actions in ReplicaMutator exception messages

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1647555 13f79535-47bb-0310-9956-ffa450edef68