baremetal: use templatefile instead of template_file data source

This commit changes the template method we use in baremetal Terraform
code responsible for generating workers Ignition configs from
template_file data source coming from 3rd party Terraform provider
to built-in 'templatefile' function, which is available from
Terraform 0.12, as it provides the exact same functionality, but
do not require downloading 3rd party provider.

Also 'template' provider recommends using this function:
https://www.terraform.io/docs/providers/template/d/file.html.

This also allows passing parameters to the template in complex types
(like lists) and call functions like 'join' inside the template, which
better separates data from how they are rendered.

Part of #196

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

assets/lokomotive-kubernetes/bare-metal/flatcar-linux/kubernetes/cl/worker.yaml.tmpl

@@ -92,7 +92,7 @@ storage:
           KUBELET_IMAGE_URL=docker://k8s.gcr.io/hyperkube
           KUBELET_IMAGE_TAG=v1.18.3
           KUBELET_IMAGE_ARGS="--exec=/usr/local/bin/kubelet"
-          NODE_LABELS="${kubelet_labels}"
+          NODE_LABELS="${join(",", [for k, v in kubelet_labels : "${k}=${v}"])}"
     - path: /etc/hostname
       filesystem: root
       mode: 0644

assets/lokomotive-kubernetes/bare-metal/flatcar-linux/kubernetes/profiles.tf

@@ -206,26 +206,18 @@ resource "matchbox_profile" "workers" {
 }
 
 data "ct_config" "worker-ignitions" {
-  count        = length(var.worker_names)
-  content      = data.template_file.worker-configs[count.index].rendered
-  pretty_print = false
-
-  # Must use direct lookup. Cannot use lookup(map, key) since it only works for flat maps
-  snippets = local.clc_map[var.worker_names[count.index]]
-}
-
-data "template_file" "worker-configs" {
   count = length(var.worker_names)
-
-  template = file("${path.module}/cl/worker.yaml.tmpl")
-
-  vars = {
+  content = templatefile("${path.module}/cl/worker.yaml.tmpl", {
     domain_name            = var.worker_domains[count.index]
     cluster_dns_service_ip = module.bootkube.cluster_dns_service_ip
     cluster_domain_suffix  = var.cluster_domain_suffix
     ssh_keys               = jsonencode(var.ssh_keys)
-    kubelet_labels         = join(",", [for k, v in merge({ "node.kubernetes.io/node" = "" }, var.labels) : "${k}=${v}"])
-  }
+    kubelet_labels         = merge({ "node.kubernetes.io/node" = "" }, var.labels),
+  })
+  pretty_print = false
+
+  # Must use direct lookup. Cannot use lookup(map, key) since it only works for flat maps
+  snippets = local.clc_map[var.worker_names[count.index]]
 }
 
 locals {