Fix get_segments_id with subnets without segment_id

Unfortunatly when we merged Ie166f3b51fddeaf916cda7c5ac34bbcdda0fd17a we
forgot that subnets can have no segment_id field.

Change-Id: Idb35b7e3c69fe8efe498abe4ebcc6cad8918c4ed
Closes-Bug: #2018375
(cherry picked from commit 6d7bd6a)
(cherry picked from commit 6b8d9d4)
(cherry picked from commit 77db642)
(cherry picked from commit 9a6a421)
(cherry picked from commit d3f44cd)

Author: sbauza

nova/network/neutron.py

@@ -3579,7 +3579,7 @@ def get_segment_ids_for_network(
                 'Failed to get segment IDs for network %s' % network_id) from e
         # The segment field of an unconfigured subnet could be None
         return [subnet['segment_id'] for subnet in subnets
-                                     if subnet['segment_id'] is not None]
+                                     if subnet.get('segment_id') is not None]
 
     def get_segment_id_for_subnet(
         self,

nova/tests/unit/network/test_neutron.py

@@ -6328,7 +6328,7 @@ def test_get_segment_ids_for_network_passes(self, mock_client):
             network_id=uuids.network_id, fields='segment_id')
 
     @mock.patch.object(neutronapi, 'get_client')
-    def test_get_segment_ids_for_network_with_no_segments(self, mock_client):
+    def test_get_segment_ids_for_network_with_segments_none(self, mock_client):
         subnets = {'subnets': [{'segment_id': None}]}
         mocked_client = mock.create_autospec(client.Client)
         mock_client.return_value = mocked_client
@@ -6343,6 +6343,22 @@ def test_get_segment_ids_for_network_with_no_segments(self, mock_client):
         mocked_client.list_subnets.assert_called_once_with(
             network_id=uuids.network_id, fields='segment_id')
 
+    @mock.patch.object(neutronapi, 'get_client')
+    def test_get_segment_ids_for_network_with_no_segments(self, mock_client):
+        subnets = {'subnets': [{}]}
+        mocked_client = mock.create_autospec(client.Client)
+        mock_client.return_value = mocked_client
+        mocked_client.list_subnets.return_value = subnets
+        with mock.patch.object(
+            self.api, '_has_segment_extension', return_value=True,
+        ):
+            res = self.api.get_segment_ids_for_network(
+                self.context, uuids.network_id)
+        self.assertEqual([], res)
+        mock_client.assert_called_once_with(self.context, admin=True)
+        mocked_client.list_subnets.assert_called_once_with(
+            network_id=uuids.network_id, fields='segment_id')
+
     @mock.patch.object(neutronapi, 'get_client')
     def test_get_segment_ids_for_network_fails(self, mock_client):
         mocked_client = mock.create_autospec(client.Client)