Fix non-existent cinder policy action tests.

The current policy actions are invalid as they are not included
in Cinder's policy.json [0] and are not enforced by Cinder's
policy enforcement system:

  - volume:list_extensions
  - volume_extension:get_volumes_image_metadata
  - volume:availability_zone_list
  - volume:get_volume_image_metadata

Some of these are incorrectly spelled:
  - volume:get_volume_image_metadata => volume:get_snapshot_metadata
  - volume_extension:get_volumes_image_metadata =>
    volume_extension:volume_image_metadata

Some of these are not enforced at all so have been removed:
  - volume:list_extensions
  - volume:availability_zone_list

Some of these are not as granular (but are not being changed due
to their being fixed in Related-Change):
  - volume_extension:qos_specs_manage:<create/update/delete/read> =>
    volume_extension:qos_specs_manage

[0] https://github.com/openstack/cinder/blob/master/etc/cinder/policy.json

Change-Id: I2d3fcdb38126df4df4e2ffe78acec7cefeba8ea3
Related-Change: I1ca996e968a273b989bea0bf3c54b47349ca47fe
Closes-Bug: #1677026
5 files changed