Add missing CannotUpdate exception

* Add missing exception CannotUpdate
* Add unit tests to verify that exception is called

Closes-Bug: #1508876
Change-Id: I9b69ac2bb683a01d5c55d11c9df2657ef23da2e8

nailgun/nailgun/api/v1/handlers/base.py

@@ -189,6 +189,8 @@ class BaseHandler(object):
             errors.NodeOffline,
             errors.NoDeploymentTasks,
             errors.UnavailableRelease,
+            errors.CannotCreate,
+            errors.CannotUpdate,
             errors.CannotDelete
         ) as exc:
             raise cls.http(400, exc.message)

nailgun/nailgun/errors/__init__.py

@@ -25,6 +25,7 @@ default_messages = {
     # REST errors
     "CannotDelete": "Can't delete object",
     "CannotCreate": "Can't create object",
+    "CannotUpdate": "Can't update object",
     "NotAllowed": "Action is not allowed",
     "InvalidField": "Invalid field specified for object",
     "ObjectNotFound": "Object not found in DB",

nailgun/nailgun/test/unit/test_objects.py

@@ -600,6 +600,23 @@ class TestNodeObject(BaseIntegrationTest):
                     template, group_name)
             )
 
+    def test_update_w_error(self):
+        self.env.create(
+            nodes_kwargs=[
+                {'roles': ['controller']},
+                {'roles': ['compute', 'cinder']}
+            ]
+        )
+        cluster_2 = self.env.create_cluster()
+
+        node_0 = self.env.nodes[0]
+        data = {
+            'cluster_id': cluster_2['id']
+        }
+
+        self.assertRaises(
+            errors.CannotUpdate, objects.Node.update, node_0, data)
+
 
 class TestTaskObject(BaseIntegrationTest):