Fix get_instance_by_id, catch NotFound appopriately

novaclient will raise a NotFound exception here instead of returning None,
which the rest of the RUG assumes.

Change-Id: I6812bd01bb4a56433bc1c408040470d3711a0005
Closes-bug: #1459445
(cherry picked from commit ceaf3ce53c)

akanda/rug/api/nova.py

@@ -18,6 +18,7 @@ from datetime import datetime
 import logging
 
 from novaclient.v1_1 import client
+from novaclient import exceptions as novaclient_exceptions
 
 from oslo.config import cfg
 
@@ -138,7 +139,10 @@ class Nova(object):
             return None
 
     def get_instance_by_id(self, instance_id):
-        return self.client.servers.get(instance_id)
+        try:
+            return self.client.servers.get(instance_id)
+        except novaclient_exceptions.NotFound:
+            return None
 
     def destroy_instance(self, instance_info):
         if instance_info:

akanda/rug/test/unit/api/test_nova_wrapper.py

@@ -21,6 +21,8 @@ import unittest2 as unittest
 from six.moves import builtins as __builtins__
 from akanda.rug.api import nova
 
+from novaclient import exceptions as novaclient_exceptions
+
 
 class FakeModel(object):
     def __init__(self, id_, **kwargs):
@@ -180,6 +182,12 @@ class TestNovaWrapper(unittest.TestCase):
         self.client.servers.get.assert_has_calls(expected)
         self.assertEquals(result, 'fake_instance')
 
+    def test_get_instance_by_id_not_found(self):
+        not_found = novaclient_exceptions.NotFound('instance_id')
+        self.client.servers.get.side_effect = not_found
+        result = self.nova.get_instance_by_id('instance_id')
+        self.assertEqual(result, None)
+
     def test_destroy_router_instance(self):
         self.nova.destroy_instance(self.INSTANCE_INFO)
         self.client.servers.delete.assert_called_with(self.INSTANCE_INFO.id_)