Additional "Unify Manager._update behaviour" cleanup

Make _update always return an instance of self.resource_class.

This is in preparation for fixing bug 1145768 by reverting the API
changes made in the original "Unify Manager._update behaviour" change.

This is to avoid needing to revert some of the cleanup that was made
in that change.

Change-Id: I842bda40a0dc168689a7dd8b88433c3cebef5839

novaclient/base.py

@@ -156,10 +156,11 @@ class Manager(utils.HookableMixin):
     def _update(self, url, body, response_key=None, **kwargs):
         self.run_hooks('modify_body_for_update', body, **kwargs)
         _resp, body = self.api.client.put(url, body=body)
-        if response_key:
-            return self.resource_class(self, body[response_key])
-        else:
-            return body
+        if body:
+            if response_key:
+                return self.resource_class(self, body[response_key])
+            else:
+                return self.resource_class(self, body)
 
 
 class ManagerWithFind(Manager):

tests/v1_1/test_floating_ips_bulk.py

@@ -61,4 +61,4 @@ class FloatingIPsBulkTest(utils.TestCase):
         fl = cs.floating_ips_bulk.delete('192.168.1.0/30')
         body = {'ip_range': '192.168.1.0/30'}
         cs.assert_called('PUT', '/os-floating-ips-bulk/delete', body)
-        self.assertEqual(fl['floating_ips_bulk_delete'], body['ip_range'])
+        self.assertEqual(fl.floating_ips_bulk_delete, body['ip_range'])