When provisioning Ubuntu systems, Foreman still uses the `/etc/network/interfaces` file. However, Ubuntu 18.04 moved away from `/etc/network/interfaces` and instead uses `/etc/netplan`.

I will add code to address this.

I previously submitted a PR in https://github.com/theforeman/community-templates/pull/568, and @Jan Pacak submitted a similar PR in https://github.com/theforeman/community-templates/pull/545. I had to give up on my PR due to work issues, but I'm picking it up again.