[WIP] update the terraform stanzas for the updated terraform provider

[displague]

This PR changes this repo to use https://github.com/displague/terraform-provider-linode which is the official provider.

[displague]

I use SSH Agent and my id_rsa is encrypted, so Terraform errors if you try to use it.

You'll notice I removed the private_key connection references so that agent will be used.

If there is a better practice on how to handle this in Terraform, I'm all ears.