Use UUID as default Keystone token format

Keystone and puppet-keystone have both changed the default token
format to UUID in Juno.  Packstack still defaults to the PKI token
format.  Packstack should have the same default as the other
components.

Change-Id: I121f7ea58c595393f58df8d7d25ce6e2ff6bfba4
Closes-bug: #1382160