[SPARK-4295][External]Fix exception in SparkSinkSuite

Handle exception in SparkSinkSuite, please refer to [SPARK-4295]
As i have no good idea about how to get a random string name, such as how to get each test case name. In getClass.getDeclaredMethods.toString, we can get different string like[Ljava.lang.reflect.Method;@5f3ef269.