- [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).
private final static Logger logger = LoggerFactory.getLogger(RegistryProtocol.class);
    private static RegistryProtocol INSTANCE;
    private final Map<URL, NotifyListener> overrideListeners = new ConcurrentHashMap<>();
    private final Map<String, ServiceConfigurationListener> serviceConfigurationListeners = new ConcurrentHashMap<>();
    private final ProviderConfigurationListener providerConfigurationListener = new ProviderConfigurationListener();
    
    
    private final Map<String, ExporterChangeableWrapper<?>> bounds = new ConcurrentHashMap<>();
    private Cluster cluster;
    private Protocol protocol;
    private RegistryFactory registryFactory;
    private ProxyFactory proxyFactory;
    public RegistryProtocol() {
        INSTANCE = this;
    }
    public static RegistryProtocol getRegistryProtocol() {
        if (INSTANCE == null) {
            ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(REGISTRY_PROTOCOL); 
        }
        return INSTANCE;