Bug fix: Do not fail on routers with no ext gw

Although I've not been able to reproduce it, some user have reported
an exception from shade in the list_router_interfaces() call when
trying to access the external_gateway_info of a router that does not
have this key set. Let's just be safe and and a check to make sure
that the key exists.

Change-Id: I949b76b2b306e5161e7ee77d6c588a77ac4c7d87

releasenotes/notes/router_ext_gw-b86582317bca8b39.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - No longer fail in list_router_interfaces() if a router does
+    not have the external_gateway_info key.

shade/openstackcloud.py

@@ -1854,9 +1854,12 @@ class OpenStackCloud(object):
 
         if interface_type:
             filtered_ports = []
-            ext_fixed = (router['external_gateway_info']['external_fixed_ips']
-                         if router['external_gateway_info']
-                         else [])
+            if ('external_gateway_info' in router and
+                'external_fixed_ips' in router['external_gateway_info']):
+                ext_fixed = \
+                    router['external_gateway_info']['external_fixed_ips']
+            else:
+                ext_fixed = []
 
             # Compare the subnets (subnet_id, ip_address) on the ports with
             # the subnets making up the router external gateway. Those ports

shade/tests/unit/test_shade.py

@@ -250,6 +250,28 @@ class TestShade(base.TestCase):
         self.cloud.delete_router('123')
         self.assertTrue(mock_client.delete_router.called)
 
+    @mock.patch.object(shade.OpenStackCloud, 'search_ports')
+    @mock.patch.object(shade.OpenStackCloud, 'neutron_client')
+    def test_list_router_interfaces_no_gw(self, mock_client, mock_search):
+        """
+        If a router does not have external_gateway_info, do not fail.
+        """
+        external_port = {'id': 'external_port_id',
+                         'fixed_ips': [
+                             ('external_subnet_id', 'ip_address'),
+                         ]}
+        port_list = [external_port]
+        router = {
+            'id': 'router_id',
+        }
+        mock_search.return_value = port_list
+        ret = self.cloud.list_router_interfaces(router,
+                                                interface_type='external')
+        mock_search.assert_called_once_with(
+            filters={'device_id': router['id']}
+        )
+        self.assertEqual([], ret)
+
     @mock.patch.object(shade.OpenStackCloud, 'search_ports')
     @mock.patch.object(shade.OpenStackCloud, 'neutron_client')
     def test_list_router_interfaces_all(self, mock_client, mock_search):