Add support for EC2 using IAM Role to access s3

This adds an optional behaviour to setup the hub to
access the s3 bucket using IAM in AWS

Author: James Naylor

terraform/aws_cloudflare/hosts.tpl

@@ -5,6 +5,7 @@ db_host = ${db_host}
 db_name = ${db_name}
 db_user = ${db_user}
 db_password = ${db_password}
+s3_useIam = ${use_iam_for_s3}
 s3_endpoint = ${s3_endpoint}
 s3_accessKeyId = ${s3_accessKeyId}
 s3_secretAccessKey = ${s3_secretAccessKey}