Clean up a relatively common potential error in XC scan

Do not clutter logs with this condition.

confluent_server/confluent/discovery/handlers/xcc.py

@@ -92,7 +92,10 @@ class NodeHandler(immhandler.NodeHandler):
         ip, port = self.get_web_port_and_ip()
         c = webclient.SecureHTTPConnection(ip, port,
             verifycallback=self.validate_cert)
-        i = c.grab_json_response('/api/providers/logoninfo')
+        try:
+            i = c.grab_json_response('/api/providers/logoninfo')
+        except Exception:
+            return
         modelname = i.get('items', [{}])[0].get('machine_name', None)
         if modelname:
             self.info['modelname'] = modelname