Fix regression in glance client call

In [0] the way parameters are passed to the glance client was changed.
Sadly one required argument was dropped during this, we need to insert
it again in order to fix e.g. rbd backend usage.

[0] https://review.openstack.org/614351

Change-Id: I5a4cfb3c9b8125eca4f6c9561d3023537e606a93
Closes-Bug: 1803717

nova/image/glance.py

@@ -482,7 +482,7 @@ class GlanceImageServiceV2(object):
         # 'show_multiple_locations' must be enabled in glance api conf file.
         try:
             return self._client.call(
-                context, 2, 'add_location', args=(image_id, location))
+                context, 2, 'add_location', args=(image_id, location, {}))
         except glanceclient.exc.HTTPBadRequest:
             _reraise_translated_exception()