Support option for Keystone PKIZ token provider

Keystone added support for a compressed token provider, PKIZ. This
change adds support to devstack. Set the KEYSTONE_TOKEN_FORMAT
option to "PKIZ" to configure Keystone to use it.

Change-Id: I123eef661c85cc805e950f1179b48e885078d40f
Merge "Support option for Keystone PKIZ token provider"