Fix parameterized class decorator

The decorator use the types.MethodType to attach the parameterized
test to the test class, but the function changed in python 3.x. This
uses six to do the right thing so this can be used outside the tempest
tests that are always run with python 2.x.

Change-Id: I56fee078d3fa718536208fd3bd5228cc45d24444

functionaltests/common/utils.py

@@ -16,8 +16,8 @@ limitations under the License.
 import collections
 import functools
 import time
-import types
 
+import six
 import netaddr
 
 
@@ -59,7 +59,7 @@ def parameterized_class(cls):
 
             # To add a method to a class, available for all instances:
             #   MyClass.method = types.MethodType(f, None, MyClass)
-            setattr(cls, new_name, types.MethodType(new_method, None, cls))
+            setattr(cls, new_name, six.create_unbound_method(new_method, cls))
     return cls