Add missing volume RBAC test

Add missing RBAC test for 'show_group_type'
API [0] which enforces "group:access_group_type_specs"
according to policy in code docs [1].
[0]https://developer.openstack.org/api-ref/block-storage/v3/#show-group-type-details
[1]https://github.com/openstack/cinder/blob/76231f3ad2828fe7bb60ecd9686db807622bbb7a/cinder/policies/group_types.py#L53

Change-Id: I71c81d0798082c03408d75deb021e7fcf077b938
1 file changed