Use six.with_metaclass to specify metaclasses

Metaclass specification is incompatible between Python 2 and 3. Use the
six.with_metaclass helper to specify metaclasses.

Reviewed-By: Petr Viktorin <pviktori@redhat.com>

ipapython/install/util.py

@@ -159,5 +159,6 @@ class InnerClassMeta(type):
             self.__outer_class__ = cls
             self.__outer_name__ = name
             self.__name__ = '.'.join((cls.__name__, name))
+            self.__qualname__ = self.__name__
 
         return cls, name