Default to PKIZ tokens

Changes the default token format to PKIZ from PKI.

Blueprint: compress-tokens

DocImpact  Changes the default Token Provider to PKIZ
           If only token_format=UUID is set, Keystone
           will not start with a warning about provider
           mismatch

Change-Id: Idf14ab6c6dd3a3cab42c35771416d9096ea4d900