Introduce scope_types in rescue server policy
Introduce scope_types in rescue server policy

oslo.policy introduced the scope_type feature which can
control the access level at system-level and project-level.
 - https://docs.openstack.org/oslo.policy/latest/user/usage.html#setting-scope
 - http://specs.openstack.org/openstack/keystone-specs/specs/keystone/queens/system-scope.html

Appropriate scope_type for nova case:
- https://specs.openstack.org/openstack/nova-specs/specs/ussuri/approved/policy-defaults-refresh.html#scope

This commit introduce scope_type for rescue server API policies
as:
- ['system', 'project'] for rescue/unrescue policy even
for unlock server locked by other policy so that operators
have option to add few project scoped role like admin to
these operation.

Also adds the test case with scope_type enabled and verify we
pass and fail the policy check with expected context.

Partial implement blueprint policy-defaults-refresh

Change-Id: Idf60a3d9aff3607739d2d3d2ff5d20877a477782

mahak/nova,openstack/nova,klmitch/nova,klmitch/nova,openstack/nova,mahak/nova,mahak/nova,openstack/nova,klmitch/nova,klmitch/nova