Refactoring optional functionals for stubs when used in more than one layers.

[didrocks]

We have some functional parameters that bubbles up in multiple layers so that we can mock entire set of features. Some examples like in https://github.com/ubuntu/adsys/pull/461 shows that it’s weird to always have functional parameters calls.

Can we do better? Find another pattern with some test stubs that we can optionally attach and pass bindly between layers? This bug is some architecture/thinking process before doing a proper refactoring around it throughout the code base.