Fix super calls in ResponseBody and ResponseBodyList

Change-Id: I616e34d1928dcd0371fb877535475d979e883b57
Closes-Bug: 1420264
diff --git a/tempest/common/service_client.py b/tempest/common/service_client.py
index 69e25e2..502d62e 100644
--- a/tempest/common/service_client.py
+++ b/tempest/common/service_client.py
@@ -90,7 +90,7 @@
         self.response = response
 
     def __str__(self):
-        body = super.__str__(self)
+        body = super(ResponseBody, self).__str__()
         return "response: %s\nBody: %s" % (self.response, body)
 
 
@@ -107,5 +107,5 @@
         self.response = response
 
     def __str__(self):
-        body = super.__str__(self)
+        body = super(ResponseBodyList, self).__str__()
         return "response: %s\nBody: %s" % (self.response, body)