Comment 3 for bug 1645175

Kevin, what release did you test this against? See the questions and comments between myself and John Garbutt in the review here:

https://review.openstack.org/#/c/452577/

In short, it seems the existing code should be working. The instance.info_cache.network_info should be getting updated after the port is attached and associated with the instance, such that when we deallocate the port on failure, the network info cache should have the preserve_on_delete flag set on that VIF in the NetworkInfo object.