L2VPN doesn't change to down after setting a link to down and reprovisioning is not possible

[gretelliz]

The status of the L2VPN doesn't change to down after setting the link to down and ensure that provisioning is not possible (see test_016_update_port_in_inter_domain_link_down_no_reprov)

[YufengXin]

@gretelliz Could you pls elaborate on this test? How is it different from the failure handling test case in the Main that passed?

[gretelliz]

See comment in issue #456