Updated openstack/openstack
Project: openstack/python-glanceclient  d833006bd4c2430d286905bc3a22004754739c98

Use immutable arg rather mutable arg

Passing mutable objects as default args is a known Python pitfall.
We'd better avoid this. This commit changes mutable default args with
None.

Change-Id: I78323383c8b6a9a516a2a217303124870822418b