Fixed the creation of EC2 VPC instances with public IPs.

Currently, though we added support for public IPs in VPC (SHA: be132d1da48fced8bc7cd774916c373ae1b9a962), I missed bumping the API version (so it's an unrecognized param :unamused:) & there's special logic around where a public IP can be applied that wasn't present in the JSON model.

Passing all tests. Review would be appreciated, especially on the change related to the numbering of the network interfaces. @jamesls @garnaat @danielgtaylor