This change adds support for the ``service`` role, which is intended
largely for service to service communiation, such as if one wanted to
utilzie a "nova" project, and have an ironic service user within it,
and then configure the ``nova-compute`` service utilizing those credentials.
Or vice versa, an "ironic" project, with a nova user.
In this case, access is exceptionally similar to the rights afforded to
a "project scoped manager" or an "owner-admin".
Change-Id: Ifd098a4567d60c90550afe5236ae2af143b6bac2
bad3790e8a