Use system_reader in identity v3 admin tests

Add RBAC support to identity v3 admin tests by introducing system_reader
credentials for read operations (list/show) while retaining admin
credentials for write operations (create/update/delete). This ensures
proper scope enforcement when keystone enforce_scope is enabled.

Implements-blueprint: test-keystone-with-srbac-defaults
Change-Id: Idb6723dd42eeec68ef115d2d8860e36abf2c5276
Signed-off-by: Abhishek Bongale <abhishekbongale@outlook.com>
12 files changed