Deployments datasource

[danafallon]

To verify:

1. Set up ~/.terraformrc:

provider_installation {

  dev_overrides {
      "artie.com/terraform/artie" = "/Users/<Username>/go/bin"
  }

  # For all other providers, install them directly from their origin provider
  # registries as normal. If you omit this, Terraform will _only_ use
  # the dev_overrides block, and so no other providers will be available.
  direct {}
}

2. Run the dashboard api server locally and put a real api key in examples/deployments/main.tf
3. go install .
4. cd examples/deployments/
5. tf plan