- [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).
*
     * @param invokerUrls this parameter can't be null
     */
    
    private void refreshInvoker(List<URL> invokerUrls) {
        Assert.notNull(invokerUrls, "invokerUrls should not be null");
        if (invokerUrls.size() == 1 && invokerUrls.get(0) != null && Constants.EMPTY_PROTOCOL.equals(invokerUrls
                .get(0)
                .getProtocol())) {
            this.forbidden = true; 
            this.invokers = Collections.emptyList();
            routerChain.setInvokers(this.invokers);
            destroyAllInvokers(); 
        } else {
            this.forbidden = false; 
            Map<String, Invoker<T>> oldUrlInvokerMap = this.urlInvokerMap; 
            if (invokerUrls == Collections.<URL>emptyList()) {
                invokerUrls = new ArrayList<>();
            }
            if (invokerUrls.isEmpty() && this.cachedInvokerUrls != null) {
                invokerUrls.addAll(this.cachedInvokerUrls);
            } else {
                this.cachedInvokerUrls = new HashSet<>();
                this.cachedInvokerUrls.addAll(invokerUrls);
            }
            if (invokerUrls.isEmpty()) {
                return;
            }
            Map<String, Invoker<T>> newUrlInvokerMap = toInvokers(invokerUrls);