Add floating IPs is broken on novaclient >= 10.0

[puck]

If people try to use novaclient >= 10.0 and try to add a floating IP then they get:

AttributeError: add_floating_ip

This patch which was merged in v10.0 of novaclient removed that method: https://review.openstack.org/#/c/459859/

[puck]

Downgrading to novaclient v9.x works.