- [x] I have searched the [issues](https://github.com/apache/incubator-dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/incubator-dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.0
* Operating System version: mac
* Java version: 1.8

### Steps to reproduce this issue

1.  `AbstractClient#initConnectStatusCheckCommand` set break point at `  !isConnected()`.
2. `AbstractClient#close()` set break point here.    
3.  start client first, start provider and then shutdown provider gracefully , let method `AbstractClient.close()` be executed. Then select step `1` and trigger the thread to execute `!isConnected`, here will always try to connect the offline machine.

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

When the server goes offline, the client will not reconnect the offline machine.

### Actual Result

What actually happens?

The client reconnects the offline machine every 2 seconds and causes a large number of arp packets(because ip is recycled and not available now).
enabled = !url.getParameter(Constants.DISABLED_KEY, false);
                    } else {
                        enabled = url.getParameter(Constants.ENABLED_KEY, true);
                    }
                    if (enabled) {
                        invoker = new InvokerDelegate<T>(protocol.refer(serviceType, url), url, providerUrl);
                    }
                } catch (Throwable t) {
                    logger.error("Failed to refer invoker for interface:" + serviceType + ",url:(" + url + ")" + t.getMessage(), t);
                }
                if (invoker != null) { 
                    newUrlInvokerMap.put(key, invoker);
                }
            } else {
                newUrlInvokerMap.put(key, invoker);
            }
        }
        keys.clear();
        return newUrlInvokerMap;
    }
    /**
     * Merge url parameters. the order is: override > -D >Consumer > Provider
     *
     * @param providerUrl
     * @return
     */
    private URL mergeUrl(URL providerUrl) {
        providerUrl = ClusterUtils.mergeUrl(providerUrl, queryMap); 
        providerUrl = overrideWithConfigurator(providerUrl);
        providerUrl = providerUrl.addParameter(Constants.CHECK_KEY, String.valueOf(false));