Added fix for ECS service-linked role (AWSServiceRoleForECS) issue

[mandatoryprogrammer]

This is a fix for the eventual-consistency issue with the ECS service-linked role AWSServiceRoleForECS. Terraform is currently unable to handle the eventually-consistent nature of the ECS service-linked role and so it fails when doing terraform apply with ECS services. In order to address this we pre-emptively create the role before running any terraform apply operations.

More info about this terraform bug can be found here:
hashicorp/terraform-provider-aws#11417

AWS eventual-consistency is an absolute bitch.

[mandatoryprogrammer]

Worth noting that this does reveal that terraform plan isn't perfect (or rather that terraform itself isn't).