Fix policy.json certificate_authority inconsistency
Fix policy.json certificate_authority inconsistency

Change the certificate_authority add_to_project, remove_from_project,
and set_preferred entries to use rule:admin instead of role:admin. This
brings these entries into consistency with their neighbors.

Closes-Bug: #1473593
Change-Id: Ibdb7512cf751b92298e350dac1689b036a6fd023

openstack/barbican,cneill/barbican,cloudkeep/barbican,cloudkeep/barbican,MCDong/barbican,openstack/barbican,cneill/barbican,MCDong/barbican