fix PLATdockertest failure

Change-Id: I01290e711b460711c3d36070c504f92700dcb02e
diff --git a/TestON/drivers/common/api/dockerapidriver.py b/TestON/drivers/common/api/dockerapidriver.py
index 2c1520d..4a874c6 100644
--- a/TestON/drivers/common/api/dockerapidriver.py
+++ b/TestON/drivers/common/api/dockerapidriver.py
@@ -251,7 +251,7 @@
             command = "{}/onos-form-cluster -u {} -p {} {}".format( cmdPath,
                                                                     user,
                                                                     passwd,
-                                                                    onosIps )
+                                                                    onosIPs )
             result = subprocess.call( command, shell=True )
             if result == 0:
                 return main.TRUE