Avoid leaving chromedriver processes cluttering the landscape after running the feature tests.

Per https://github.com/seleniumhq/selenium-google-code-issue-archive/issues/3378, we were doing it wrong :-(

web/regression/feature_utils/app_starter.py

@@ -33,5 +33,5 @@ class AppStarter:
         self.driver.get("http://" + self.app_config.DEFAULT_SERVER + ":" + random_server_port)
 
     def stop_app(self):
-        self.driver.close()
+        self.driver.quit()
         os.killpg(os.getpgid(self.pgadmin_process.pid), signal.SIGTERM)