Neutron is in a process to migrate to policy-in-code.
DevStack needs to be able to handle both cases with and
without policy.json in the neutron repo.
Note that nova assumes neutron API access with admin
so user_name:neutron needs to be included in context_is_admin
to make DevStack work properly. Hopefully this can be cleanup
but this is a separate topic from policy-in-code.
Needed-By: https://review.openstack.org/#/c/585037/
Change-Id: Id1b0600d92e839ade1790a15c372e82e8e16ee9f
80769c5714