Convert Terraform plugin to use helper

[lucywyman]

Use Case

The Terraform plugin should use the ruby plugin helper library. We should wait to release this until other plugins are converted

Additional Context

With the addition of the plans/tasks in GH-1360 puppetlabs/puppetlabs-terraform#4 the plan/task parameters map to terraform CLI options. The resolve_reference task uses statefile for state, we should update it to match the CLI and roll that breaking change into the target_mapping breaking change.

[donoghuc]

$ terraform state show --help
Usage: terraform state show [options] ADDRESS

  Shows the attributes of a resource in the Terraform state.

  This command shows the attributes of a single resource in the Terraform
  state. The address argument must be used to specify a single resource.
  You can view the list of available resources with "terraform state list".

Options:

  -state=statefile    Path to a Terraform state file to use to look
                      up Terraform-managed resources. By default it will
                      use the state "terraform.tfstate" if it exists.

[beechtom]

PR: puppetlabs/puppetlabs-terraform#6

[donoghuc]

Closed by puppetlabs/puppetlabs-terraform#6