This patch added Py4jCallbackConnectionCleaner to clean the leak sockets of Py4J every 30 seconds. This is a workaround before Py4J fixes the leak issue https://github.com/bartdag/py4j/issues/187

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10579 from zsxwing/SPARK-12617.