Add support for containerd-based images

[detiber]

Currently wardroom bakes images that use docker, we should add the ability to generate images that use containerd instead.

[vincepri]

This is being worked on here kubernetes-sigs/cluster-api-provider-aws#25 and can be ported here after testing.

[scottslowe]

I know that @vincepri said there's some work happening in cluster-api, but I have a branch I can submit as a PR (based on Vince's work) if we'd like to go ahead and close this out.

[detiber]

@scottslowe that would be great, we just haven't had the time to verify the containerd changes do not break the swizzle workflows yet :)

[scottslowe]

@detiber I haven't tested the swizzle workflows, either. I think @craigtracey may have some changes for the swizzle workflows that he has yet to check in. I'll check with him on the status of those changes so that we can see if we should test now or wait for his changes.

[stevesloka]

Why do we have the same code in multiple repos and copy/paste between them? Can't we standardize on Wardroom?

[detiber]

@stevesloka long term we'd like to standardize the image baking and contribute upstream. Currently we contributed that for cluster-api-provider-aws, but the plan is to try and make it more generally available for the cluster-api.

The main issue with standardizing on Wardroom has been that the scope of this repo has grown beyond just image baking and testing/validating that changes do not break the existing workflows for those additional uses is difficult (such as these containerd changes, which impact the swizzle workflows).