Code review comment for autopkgtest-cloud:i386-as-amd64-cross

Steve, can I nudge you to address these review comments please? It's clear now that we should make this apply to all releases >= focal. At the start of the hirsute cycle, because this is currently cowboyed on the production infrastructure and requires manual editing, I made a mistake and all i386 tests ran as amd64 for a few days. Now this is fixed but we have regressions reported that need to be manually hinted away.

We should not be in this position again - both because there's no cowboy and because it doesn't require adjustment at each opening.

Here's a "release_ge" script I wrote for something else, which you can use like "if release_ge ${RELEASE} focal; then ... fi" in create-nova-image-new-release, to inject the --add-architecture only when needed.

https://gist.github.com/iainlane/a6df7f4c8e928fd7d1cccc6bef643211