Use ddt for existing policy tests
Use ddt for existing policy tests

This change aims to replicate the existing policy check tests using
ddt so that they can be represented in a declarative format.

The number of tests are expected to grow significantly with
secure-rbac, so the aim of this change is to explore how best to
represent the tests before the new tests are written.

Change-Id: Id1b60f5525773eadbe1b85797eeefdb70d73ae1d

openstack/ironic,openstack/ironic