[mungegithub] Set up an E2E test for the bot

[foxish]

With the right use of fakes and mocks, we should be able to setup a comprehensive e2e test for the bot, so that we can make changes more confidently. This should go hand in hand with the canary style of deployment, and a standard deployment plan for the submit-queue.

[foxish]

We should probably move to the dedicated kubernetes/pr-bot repository first, before we do this. #762 (comment)

[apelisse]

Yes, we could improve that, it would be very sweet.

[foxish]

This is really hard and I question whether it is worth doing considering how reliant it is on github's API.