[WIP] Allow specification of the bootscript

[stephenmoloney]

What does this commit/MR/PR do?

• Allow specification of the bootscript
• Remove the unused additional volume - those aren't needed with baremetal servers

Why is this commit/MR/PR needed?

• Allow usage of alternate kernels

[stephenmoloney]

I would prefer this feature to be entirely optional and be a null terraform variable by default.

Terraform 12 when released will support this and I think it's a good way to go. See hashicorp/terraform/issues/14037#issuecomment-433569957

It would require changing terraform to

terraform {
  required_version = ">= 0.12"
}

once it's released that is.

I'll put this on hold for now.