Use list instead of six.viewkeys to avoid py2 to py3 problems

This change fixes an 'RuntimeError: dictionary changed size during
iteration' error that is raised because of different behaviour between
python2 and python3.  An earlier attempt [1] to use the six library did
not fix the issue.

[1] https://review.opendev.org/660427

Resolves-Bug: #1829304
Change-Id: Ic4c5790a5d66e10a606327f4f4e4c92611f161d8
(cherry picked from commit a65ae9c81e)

neutron/pecan_wsgi/hooks/policy_enforcement.py

@@ -19,7 +19,6 @@ from oslo_log import log as logging
 from oslo_policy import policy as oslo_policy
 from oslo_utils import excutils
 from pecan import hooks
-import six
 import webob
 
 from neutron._i18n import _
@@ -122,7 +121,7 @@ class PolicyHook(hooks.PecanHook):
                 original_resources.append(resource_obj)
                 obj = copy.copy(resource_obj)
                 obj.update(item)
-                obj[const.ATTRIBUTES_TO_UPDATE] = six.viewkeys(item)
+                obj[const.ATTRIBUTES_TO_UPDATE] = list(item)
                 # Put back the item in the list so that policies could be
                 # enforced
                 resources_copy.append(obj)
@@ -224,7 +223,7 @@ class PolicyHook(hooks.PecanHook):
         to see them.
         """
         attributes_to_exclude = []
-        for attr_name in six.viewkeys(data):
+        for attr_name in list(data):
             # TODO(amotoki): All attribute maps have tenant_id and
             # it determines excluded attributes based on tenant_id.
             # We need to migrate tenant_id to project_id later