use config buffer size

use config buffer size

https://github.com/apache/incubator-wayang/blob/d859a97d43a8c3c3c964150eaff8f3833e41ea75/wayang-api/wayang-api-python/src/main/java/org/apache/wayang/api/python/executor/ProcessReceiver.java#L34

```java

/*
* 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.wayang.api.python.executor;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.net.Socket;
import java.util.Iterator;
/*TODO cannot be always string, include definition for every operator
* like: map(udf, inputtype, outputtype)*/
public class ProcessReceiver {

private ReaderIterator iterator;

public ProcessReceiver(Socket socket){
try{
//TODO use config buffer size
int BUFFER_SIZE = 1 * 1024;

DataInputStream stream = new DataInputStream(new BufferedInputStream(socket.getInputStream(), BUFFER_SIZE));
this.iterator = new ReaderIterator<>(stream);

} catch (IOException e) {
e.printStackTrace();
}
}

public Iterable getIterable(){
return () -> iterator;
}

public void print(){
iterator.forEachRemaining(x -> System.out.println(x.toString()));

}
}

```

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