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

### Environment

* Dubbo version: 2.7.2
* Operating System version: macOS 10.12.6
* Java version: 1.8

### Steps to reproduce this issue



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

### Expected Result

What do you expected from the above steps？

```java

    ZookeeperDynamicConfiguration(URL url, ZookeeperTransporter zookeeperTransporter) {
        this.url = url;
        rootPath = "/" + url.getParameter(CONFIG_NAMESPACE_KEY, DEFAULT_GROUP) + "/config";

        initializedLatch = new CountDownLatch(1);
        this.cacheListener = new CacheListener(rootPath, initializedLatch);
        this.executor = Executors.newFixedThreadPool(1, new NamedThreadFactory(this.getClass().getSimpleName(), true));

        zkClient = zookeeperTransporter.connect(url);
        zkClient.addDataListener(rootPath, cacheListener, executor);
        try {
            // Wait for connection
            this.initializedLatch.await();
        } catch (InterruptedException e) {
            logger.warn("Failed to build local cache for config center (zookeeper)." + url);
        }
    }
```

`        zkClient = zookeeperTransporter.connect(url);`会通过URL中的client参数来正确选择自适应扩展来初始化zk客户端。但在初始化配置中心的时候，URL是由ConfigCenterConfig得到的，此时URL中无client的信息，所以这个地方创建zk还是用的默认的zkClient。希望和注册中心时候一样获取自己扩展的zkClient


### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

RegistryConfig registryConfig = new RegistryConfig();
                            registryConfig.refresh();
                            return Arrays.asList(registryConfig);
                        })
                );
            }
        } else {
            String[] ids = COMMA_SPLIT_PATTERN.split(registryIds);
            List<RegistryConfig> tmpRegistries = CollectionUtils.isNotEmpty(registries) ? registries : new ArrayList<>();
            Arrays.stream(ids).forEach(id -> {
                if (tmpRegistries.stream().noneMatch(reg -> reg.getId().equals(id))) {
                    tmpRegistries.add(ConfigManager.getInstance().getRegistry(id).orElseGet(() -> {
                        RegistryConfig registryConfig = new RegistryConfig();
                        registryConfig.setId(id);
                        registryConfig.refresh();
                        return registryConfig;
                    }));
                }
            });
            if (tmpRegistries.size() > ids.length) {
                throw new IllegalStateException("Too much registries found, the registries assigned to this service " +
                        "are :" + registryIds + ", but got " + tmpRegistries.size() + " registries!");
            }
            setRegistries(tmpRegistries);
        }
    }
    private void loadRegistriesFromBackwardConfig() {
        // 
        // 
        if (registries == null || registries.isEmpty()) {