Terraform 0.12.x Upgrade

[mcalhoun]

This PR makes all modules and examples compatible with Terraform 0.12.x.

Please note that this change is BACKWARDS INCOMPATIBLE and you MUST use Terraform 0.12.x and above with the code once this has been merged.

[andrewward]

Had to modify this to keep my module invocation the same. Does that seem correct?

Sample code:

cluster_extra_tags = [
    {
      key                 = "Environment"
      value               = var.environment
      propagate_at_launch = true
    }
  ]

My modification:

dynamic "tag" {
    for_each = [for s in var.cluster_extra_tags: {
      key                 = s.key
      value               = s.value
      propagate_at_launch = s.propagate_at_launch
    }]

    content {
      key                 = tag.value.key
      value               = tag.value.value
      propagate_at_launch = tag.value.propagate_at_launch
    }
  }