Fix term names according to specification.

This should closes #38. Now I get:

* Secgroup:
    Category: 38; scheme="http://schemas.openstack.org/infrastructure/security/group#"; (...)
* Image:
    Category: 3ef6bb0c-6a17-47c9-a949-70256eb6651e; scheme="http://schemas.openstack.org/template/os# (...)
* Flavor:
    Category: m1.medium; scheme="http://schemas.openstack.org/template/resource#" (...)

Is this enough?