SOLR-4716,SOLR-4584: SolrCloud request proxying does not work on Tomcat and perhaps other non Jetty containers.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_3@1469677 13f79535-47bb-0310-9956-ffa450edef68