SOLR-5761: HttpSolrServer has a few fields that can be set via setters but are not volatile. (merged branch_4x r1573443)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_7@1581171 13f79535-47bb-0310-9956-ffa450edef68