oo-accept-systems: Fix check_nodes_cartridges

Fix the `check_nodes_cartridges` test in `oo-accept-systems` to get the list of cartridges the correct way rather than trying to use the `cart_list` fact, which has been deprecated for several releases.
    
With commit 4e94c47a381f3cfd168e9add0383414202aa96e5, the `cart_list` fact is no longer updated, so the check was essentially a no-op (no nodes would respond with the fact, so the `carts_for` Hash would remain empty, which would cause the test to terminate silently).

This commit fixes bug 1118908.