The tf-elastx_cleanup test job was failed with error message:
Port xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx cannot be deleted
directly via the port API: has device owner network:router_interface.
That means necessary to remove a subnet from the router before
deleting the port.
This adds a method to removes a subnet from the router automatically.
Kenichi Omichi
Victor Morales
Maxime Guyot