Use kubernetes provider to manage aws auth (#355)

This commit changes the way aws auth is managed. Before a local file
was used the generate the template and a null resource to apply it. This
is now switched to the terraform kubernetes provider.

templates/worker-role.tpl

@@ -1,8 +1,8 @@
-    - rolearn: ${worker_role_arn}
-      username: system:node:{{EC2PrivateDNSName}}
-      groups:
-        - system:bootstrappers
-        - system:nodes
-        %{~ if platform == "windows" ~}
-        - eks:kube-proxy-windows
-        %{~ endif ~}
+- rolearn: ${worker_role_arn}
+  username: system:node:{{EC2PrivateDNSName}}
+  groups:
+    - system:bootstrappers
+    - system:nodes
+    %{~ if platform == "windows" ~}
+    - eks:kube-proxy-windows
+    %{~ endif ~}