Arch-{in,}dependent dummy package

The dummypackage that we currently use to test the pipeline has some drawbacks. It is arch-independent only, so we cannot really test the test-build-all job. It is also written in python, so python3 & friends got installed during the extract-source test job on the gbp image. To summarize, it would be great to have another dummypackage that:

produces architecture independent and dependent binary packages
depends only on base packages

Any other input?

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