Compute server metadata rbac tests

Add rbac tests for the compute server metadata API [0] whose
policy definitions can be found here [1].

[0] https://developer.openstack.org/api-ref/compute/#server-metadata-servers-metadata
[1] https://github.com/openstack/nova/blob/master/nova/policies/server_metadata.py

Change-Id: Ifb8901bce0965e4a763814b29ab1d3a16d9021d9
2 files changed