Fix NAT and make it working for Terraform and Vagrant

Commit b504810 introduced a NAT to make worker capable of reaching the
public internet via the provisioner.

But it also introduced a bug, it only works for the Vagrant setup as
Manny pointed out:

https://github.com/tinkerbell/sandbox/pull/33#issuecomment-759651035

This is an attempt to fix it

Signed-off-by: Gianluca Arbezzano <gianarb92@gmail.com>

deploy/terraform/main.tf

@@ -66,6 +66,14 @@ resource "null_resource" "tink_directory" {
     destination = "/root/tink"
   }
 
+  provisioner "remote-exec" {
+    inline = [
+      "iptables -A FORWARD -i eth1 -o bond0 -j ACCEPT",
+      "iptables -A FORWARD -i bond0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT",
+      "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE",
+    ]
+  }
+
   provisioner "remote-exec" {
     inline = [
       "chmod +x /root/tink/*.sh /root/tink/deploy/tls/*.sh"