Apply six for metaclass

__metaclass__ cannot be used in python3.
six be used in general for python 3 compatibility.

Change-Id: I1d21c82163a1c00bbf4fbf3c9dd513f1c0591b00
Closes-Bug: #1236648

cinder/api/openstack/wsgi.py

@@ -29,6 +29,7 @@
 from cinder import wsgi
 
 from lxml import etree
+import six
 from xml.dom import minidom
 from xml.parsers import expat
 
@@ -1027,11 +1028,10 @@ def __new__(mcs, name, bases, cls_dict):
                                                        cls_dict)
 
 
+@six.add_metaclass(ControllerMetaclass)
 class Controller(object):
     """Default controller."""
 
-    __metaclass__ = ControllerMetaclass
-
     _view_builder_class = None
 
     def __init__(self, view_builder=None):

cinder/keymgr/key.py

@@ -25,12 +25,13 @@ class to represent all encryption keys. The basis for this class was copied
 
 import abc
 
+import six
 
+
+@six.add_metaclass(abc.ABCMeta)
 class Key(object):
     """Base class to represent all keys."""
 
-    __metaclass__ = abc.ABCMeta
-
     @abc.abstractmethod
     def get_algorithm(self):
         """Returns the key's algorithm.

cinder/keymgr/key_mgr.py

@@ -20,16 +20,17 @@
 
 import abc
 
+import six
 
+
+@six.add_metaclass(abc.ABCMeta)
 class KeyManager(object):
     """Base Key Manager Interface
 
     A Key Manager is responsible for managing encryption keys for volumes. A
     Key Manager is responsible for creating, reading, and deleting keys.
     """
 
-    __metaclass__ = abc.ABCMeta
-
     @abc.abstractmethod
     def create_key(self, ctxt, algorithm='AES', length=256, expiration=None,
                    **kwargs):

cinder/taskflow/patterns/base.py

@@ -19,6 +19,8 @@
 import abc
 import threading
 
+import six
+
 from cinder.openstack.common import uuidutils
 
 from cinder.taskflow import decorators
@@ -27,6 +29,7 @@
 from cinder.taskflow import utils
 
 
+@six.add_metaclass(abc.ABCMeta)
 class Flow(object):
     """The base abstract class of all flow implementations.
 
@@ -45,8 +48,6 @@ class Flow(object):
     - soft_reset
     """
 
-    __metaclass__ = abc.ABCMeta
-
     # Common states that certain actions can be performed in. If the flow
     # is not in these sets of states then it is likely that the flow operation
     # can not succeed.

cinder/taskflow/task.py

@@ -18,15 +18,16 @@
 
 import abc
 
+import six
+
 from cinder.taskflow import utils
 
 
+@six.add_metaclass(abc.ABCMeta)
 class Task(object):
     """An abstraction that defines a potential piece of work that can be
     applied and can be reverted to undo the work as a single unit.
     """
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, name):
         self.name = name
         # An *immutable* input 'resource' name set this task depends