Fix default entries attribute for policies

For policies entries attribute "default" expected to be
dict in contrail-api.

Change-Id: I80673315dc80d3f9a0f3e76441c3a590e37f298c
Closes-bug: #1778518

neutron_plugin_contrail/extensions/policy.py

@@ -47,7 +47,7 @@ class PolicyNotFound(NotFound):
                       'required_by_policy': True,
                       'is_visible': True},
         'entries': {'allow_post': True, 'allow_put': True,
-                    'is_visible': True, 'default': ''},
+                    'is_visible': True, 'default': {}},
         'nets_using': {'allow_post': False, 'allow_put': False,
                        'is_visible': True, 'default': ''},
     },