Some of the endpoints are *highly* restricted in ironic's newer
more stringently enforced RBAC world. Some of these endpoints would
emit 500s by default, when realistically it was the policy definition
saying "only system scope could be used" for the endpoint, but the
reality is that 403 is what should have been returned for a client to
properly understand what is going on.
Change-Id: If5e13764dad886ba3ee1a848f3ff9f3279f4d7f6
c6a4005049