[Web UI]Make decision order of Worker's WebUI port consistent with Master's

The decision order of Worker's WebUI port is "--webui-port", SPARK_WORKER_WEBUI_POR, 8081(default), spark.worker.ui.port. But in Master, the order is "--webui-port", spark.master.ui.port, SPARK_MASTER_WEBUI_PORT and 8080(default).

So we change the order in Worker's to keep it consistent with Master.