Skip the deprecated API extensions policy tests

A new policy feature flag called
``[policy_feature_flag].removed_nova_policies_stein``
has been added to Patrole's config to handle Nova API
extension policies removed in Stein [0].

The policy feature flag is applied to tests that validate
response bodies for expected attributes previously returned
for the following policies that passed authorization:

      - os_compute_api:os-config-drive
      - os_compute_api:os-extended-availability-zone
      - os_compute_api:os-extended-status
      - os_compute_api:os-extended-volumes
      - os_compute_api:os-keypairs
      - os_compute_api:os-server-usage
      - os_compute_api:os-flavor-rxtx
      - os_compute_api:os-flavor-access (only from /flavors APIs)
      - os_compute_api:image-size

Note that not all removed policies are included above because
test coverage is missing for them (like
os_compute_api:os-security-groups).

Also fixes test flows associated with image_size tests:

* endpoints are list images with details and show image (not
  list image)
* both tests should check for OS-EXT-IMG-SIZE:size attribute

[0] https://review.openstack.org/#/c/586872/8

Story: 2003501

Change-Id: Ia6f8d255a540f7063beedd80a3ca1833f3987490
7 files changed