adding terraform references for some buckets

[ryandeivert]

to: @airbnb/streamalert-maintainers

Background

A race condition could cause errors like:

Error: Error putting S3 notification configuration: NoSuchBucket: The specified bucket does not exist
	status code: 404, request id: 5A5ACCB6EB4055B8, host id: vIlTAABEslxBZXQXmF5QRhFi6z4kQ0wW2YUeJdMLKjGpJn4u5irjwctlzAPPDIY1RKsktnKyh5s=
  on modules/tf_athena/main.tf line 100, in resource "aws_s3_bucket_notification" "bucket_notification":
 100: resource "aws_s3_bucket_notification" "bucket_notification" {
...

Changes

• Using references to terraform resources/outputs for bucket names to enforce the creation of the resources before we try to use their "value".

Testing

Updates to unit tests.

[coveralls]

Coverage increased (+0.005%) to 95.43% when pulling 3a6752b on ryandeivert-adding-tf-bucket-refs into b552a05 on release-3-2-0.

[Ryxias]

If it works, it isn't stupid

That said, would this be a candidate for using a depends_on block?

[ryandeivert]

@Ryxias a reference to a resource is an implicit depends_on.. actually, depends_on should rarely be needed at all (if ever in most of our cases). see here:

Most resource dependencies are handled automatically. Terraform analyses any expressions within a resource block to find references to other objects, and treats those references as implicit ordering requirements when creating, updating, or destroying resources. Since most resources with behavioral dependencies on other resources also refer to those resources' data, it's usually not necessary to manually specify dependencies between resources.