Add update tests for policies and rules

Add update tests for policies and rules

This patch adds tests for 'update' for both policies and rules. This
completes the CRUD tests and leaves the association/disassociation for
a later patch. Note that deleting a rule isn't tested explicitly
because of a bug with the rule delete logic on the server side. Once
that code is fixed, the test should be added.

to_dict() for policies should also convert any rules inside rule lists
to dicts too, otherwise API layer receives rule object __repr__ strings
instead of actual dicts. This patch introduces a fix to the existing
to_dict() code to properly support policies.

This patch also modifies the base infra to create policies and rules for
admins and not for tenant.

Partially-Implements: blueprint quantum-qos-api
Change-Id: I13870680d7756be9dd020135bc8e91d1c12f728d
Co-Authored-By: Ihar Hrachyshka <ihrachys@redhat.com>