Fix the repo name for testing the Travis tagger

The travis auto tagger pushes a release tag to the repository when the
build (on master) is successful.

The script allows you to test it in local mode. To do so, you need to
fake the repo name (which would normally come from the Travis
environment)

This fixes the repo name to be `alphagov/performanceplatform-collector` rather
than `alphagov/stagecraft` and adds a testing commit from the repo,
rather than from the stagecraft repo.
Move function to more obvious place

If someone copies this file to another repo, they have to modify a few
variables (see previous commit).

Make these more obvious by moving them to the top of the file.
Merge pull request #9 from alphagov/fix-travis-tagger-in-test-mode

Fix the repo name for testing the Travis tagger