- [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!
```

if (!hasMethod) {
                    throw new IllegalStateException("The interface " + interfaceClass.getName()
                            + " not found method " + methodName);
                }
            }
        }
    }
    /**
     * Legitimacy check and setup of local simulated operations. The operations can be a string with Simple operation or
     * a classname whose {@link Class} implements a particular function
     *
     * @param interfaceClass for provider side, it is the {@link Class} of the service that will be exported; for consumer
     *                       side, it is the {@link Class} of the remote service interface that will be referenced
     */
    void checkMock(Class<?> interfaceClass) {
        if (ConfigUtils.isEmpty(mock)) {
            return;
        }
        String normalizedMock = MockInvoker.normalizeMock(mock);
        if (normalizedMock.startsWith(RETURN_PREFIX)) {
            normalizedMock = normalizedMock.substring(RETURN_PREFIX.length()).trim();
            try {
                //
                MockInvoker.parseMockValue(normalizedMock);
            } catch (Exception e) {
                throw new IllegalStateException("Illegal mock return in <dubbo:service/reference ... " +
                        "mock=\"" + mock + "\" />");
            }
        } else if (normalizedMock.startsWith(THROW_PREFIX)) {
            normalizedMock = normalizedMock.substring(THROW_PREFIX.length()).trim();