- [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).
throw new IllegalArgumentException("The registry export url is null! registry: " + originInvoker.getUrl());
        }
        return URL.valueOf(export);
    }
    /**
     * Get the key cached in bounds by invoker
     *
     * @param originInvoker
     * @return
     */
    private String getCacheKey(final Invoker<?> originInvoker) {
        URL providerUrl = getProviderUrl(originInvoker);
        String key = providerUrl.removeParameters("dynamic", "enabled").toFullString();
        return key;
    }
    @Override
    @SuppressWarnings("unchecked")
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        url = url.setProtocol(url.getParameter(REGISTRY_KEY, DEFAULT_REGISTRY)).removeParameter(REGISTRY_KEY);
        Registry registry = registryFactory.getRegistry(url);
        if (RegistryService.class.equals(type)) {
            return proxyFactory.getInvoker((T) registry, type, url);
        }
        
        Map<String, String> qs = StringUtils.parseQueryString(url.getParameterAndDecoded(REFER_KEY));
        String group = qs.get(Constants.GROUP_KEY);
        if (group != null && group.length() > 0) {
            if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
                return doRefer(getMergeableCluster(), registry, type, url);
            }