This change is the first step to support secure RBAC and allows usage
of system scope credentials for Keystone API request.
This change covers the following two items.
- assignment of system scope roles to system user
- credential parameters for authtoken middleware
Depends-on: https://review.opendev.org/804325
Change-Id: I2a54b0d0c03a98b3fe7a3a4a28051247eea7e70a