HMaster redirect should sanity check user input

  public static class RedirectServlet extends HttpServlet {
    private static final long serialVersionUID = 2894774810058302472L;
    private static int regionServerInfoPort;

    @Override
    public void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
      String redirectUrl = request.getScheme() + "://"
        + request.getServerName() + ":" + regionServerInfoPort
        + request.getRequestURI();
      response.sendRedirect(redirectUrl);
    }
  }