- [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: 2.7.2-SNAPSHOT
* Operating System version: windows1
* Java version: 1.8

### Steps to reproduce this issue
```java
public class RedisMetadataReport extends AbstractMetadataReport {

    private final static Logger logger = LoggerFactory.getLogger(RedisMetadataReport.class);

    final JedisPool pool;

    public RedisMetadataReport(URL url) {
        super(url);
        pool = new JedisPool(new JedisPoolConfig(), url.getHost(), url.getPort());
    }
}
```
I see the construct method used `JedisPool`, 
**if cluster ，how should  do？**

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.dubbo.metadata.identifier;
import org.apache.dubbo.common.URL;
import static org.apache.dubbo.common.constants.CommonConstants.ANY_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.APPLICATION_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.GROUP_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PATH_SEPARATOR;
import static org.apache.dubbo.common.constants.CommonConstants.SIDE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.VERSION_KEY;
/**
 * 2018/10/25
 */
public class MetadataIdentifier {