The policy enforcement of Nova v2.1 API get improvement.
Policy only enforce at the entry of API.
Without duplicated rules for single one API anymore.
All the v2.1 API policy rule use 'os_compute_api' as prefix which distinguish with v2 API.
Due to hard-code permission checks at db layer, part of Nova API isn't configurable by policy before. It's always required admin user. Part of Nova v2.1 API's hard-code permission checks is removed which make API policy configurable. The rest of hard-code permission checks will be removed at Liberty.