The current behavior of the aws_route53_record resource is to overwrite the record if one already exists. For example, we suppose that the notexample.com CNAME to foo.bar is added by hand via the CLI. If the new Terraform resource with the same name but with a different CNAME value is added, the record is going to be overridden. This might be a big problem: a record might be changed by mistake.

So this PR proposes to add an option named allow_overwrite on the resource to protect overwrite. When the option is true the CREATE mode is used instead of UPSERT in the change batch. This means that if an added record already exists on route53, the application will fail. By default, the overwrite is permitted to avoid compatibility issue.

…nning parallelized testing