CBQE-2020 fix url in S3 to download build in EC2

Change-Id: I21d1f12db667304029062761d6154e62bb729086
Reviewed-on: http://review.couchbase.org/33457
Tested-by: Thuan Nguyen <soccon@gmail.com>
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>