Chris,
Thanks for that. I'm very happy to create the key pair and the entry in known_hosts. In fact I did that already and had to hack the github url to reproduce the issue. The '/usr/bin/yes' thing is pretty funny. :)
I raised the bug more so you guys had some feedback. Given that the .deb package creates the 'cruise' user, I'd expect that that Cruise ought to verify that the cruise user has a fighting chance of connecting to GitHub (I guess the majority of your Git users would be using GH. Perhaps either creating the private key at package install time, and attempting to connect to GH? Or presenting the user with the steps you outline?
Best
J.