HADOOP-10255. Rename HttpServer to HttpServer2 to retain older HttpServer in branch-2 for compatibility. Merged from r1561966 in branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.3@1562616 13f79535-47bb-0310-9956-ffa450edef68