use default thing name

aws-iot-device-sdk-java/src/test/java/com/amazonaws/services/iot/client/AWSIotMqttClientIntegrationUtil.java

@@ -16,7 +16,7 @@
 public class AWSIotMqttClientIntegrationUtil {
 
     public static final String CLIENT_ENDPOINT = System.getProperty("clientEndpoint");
-    private static final String CLIENT_ID = UUID.randomUUID().toString();
+    private static final String CLIENT_ID = System.getProperty("clientId");
 
     public static final String AUTH_MODE = System.getProperty("authMode");