Python 3: Fix a TypeError in policy.py

Fix "TypeError: 'filter' object is not subscriptable" with python 3.

Blueprint: neutron-python3
Change-Id: Ia49ce2e283ecf4da5333b95006746cb19490fde4

neutron/policy.py

@@ -111,7 +111,7 @@ def _build_subattr_match_rule(attr_name, attr, action, target):
     # typing for API attributes
     # Expect a dict as type descriptor
     validate = attr['validate']
-    key = filter(lambda k: k.startswith('type:dict'), validate.keys())
+    key = list(filter(lambda k: k.startswith('type:dict'), validate.keys()))
     if not key:
         LOG.warn(_LW("Unable to find data type descriptor for attribute %s"),
                  attr_name)

tox.ini

@@ -195,6 +195,7 @@ commands = python -m testtools.run \
     neutron.tests.unit.agent.linux.test_ip_link_support \
     neutron.tests.unit.agent.linux.test_interface \
     neutron.tests.unit.test_auth \
+    neutron.tests.unit.test_policy \
     neutron.tests.unit.extensions.v2attributes \
     neutron.tests.unit.extensions.test_l3_ext_gw_mode \
     neutron.tests.unit.extensions.test_extra_dhcp_opt \