SOLR-5874: Unsafe cast in CloudSolrServer's RouteException. Change RouteException to handle Throwable rather than Exception.
SOLR-5899: CloudSolrServer's RouteResponse and RouteException should be publicly accessible.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1580553 13f79535-47bb-0310-9956-ffa450edef68