code: public JenkinsServer quietDown() throws IOException {
          try {
              client.post("/quietDown/");
          } catch (org.apache.http.client.ClientProtocolException e) {
              LOGGER.error("quietDown()", e);
          }
          return this;
      }
docs: Sends the Quiet Down (Prepare for shutdown) message
  
  @throws IOException in case of an error.