[config] Add fake script to mock integration This will allow for proper testing of the changes to the milestone_roller. Bug: 123410 Change-Id: I6c25b5572e570d4b33bb95d1e78ffceba882e51f Reviewed-on: https://fuchsia-review.googlesource.com/c/infra/roller-tests/integration/+/817271 Reviewed-by: Anthony Fandrianto <atyfto@google.com> Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com> Fuchsia-Auto-Submit: Catherine Duncan <catduncan@google.com>