Use auth_token from keystonemiddleware

This changes swift proxy-server conf to use the
keystone authtoken middleware from the
keystonemiddleware project. auth_token in
keystoneclient has been deprecated.

The corresponding change was made to swift in this patch:
https://review.openstack.org/#/c/109047/

Change-Id: I58dad8e1151067bf8df37e511fff5fc0e3dfb487
Merge "Use auth_token from keystonemiddleware"