Updated openstack/openstack
Project: openstack/python-keystoneclient  c9ae9d1fa267653c1779a9a17613bd287f1297a3

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, then use 'arg = arg or []'.

Change-Id: I52a37bbc129fab40a99c919a837147d663941dce