Currently if target is not passed in context.can(),
it use defauls target which is context.user_id, context.project_id.
These defaults target are not useful as it pass the
context's user_id and project_id only which means we tell
oslo policy to verify the context data with context data.
This commit pass the actual target for os-instance-usage-audit-log
policies which is empty dict because policy rule is system scoped rather
than project, so the token scope check deals with the required
Partial implement blueprint policy-defaults-refresh