Change the argument names used for common Keystone authentication per the
updated http://wiki.openstack.org/CLIAuth:
--auth_url -> --os_auth_url
--password -> --os_password
--username -> --os_username
--tenant_name -> os_tenant_name
--region_name -> os_region_name
All old args are depricated but available for backward compatibility.
Fixes bug 954531
Change-Id: Ic67c447e4e4b8d793f587c789cecd149446194f3