Fix unpack error in test_list_servers_detailed_filter_by_image

Change-Id: I0727bd28c7a4147084454a96271563bd4a113cec
diff --git a/tempest/api/compute/servers/test_list_server_filters.py b/tempest/api/compute/servers/test_list_server_filters.py
index bfba105..28ad83c 100644
--- a/tempest/api/compute/servers/test_list_server_filters.py
+++ b/tempest/api/compute/servers/test_list_server_filters.py
@@ -185,7 +185,7 @@
     def test_list_servers_detailed_filter_by_image(self):
         # Filter the detailed list of servers by image
         params = {'image': self.image_ref}
-        resp, body = self.client.list_servers_with_detail(params)
+        body = self.client.list_servers_with_detail(params)
         servers = body['servers']
 
         self.assertIn(self.s1['id'], map(lambda x: x['id'], servers))