Code review comment for lp://qastaging/~tealeg/landscape-client/mocker-replace-test-changer

I've addressed the comments it's viable to address.

Combining the with statements has complications that make it undesirable (I spent quite a lot of time trying to find the nicest way to do this). It could still be done in a single "with" but it would require line break escaping, and I don't think it brings us enough to justify the ugliness.