Added alternative builder for project images: buildah
https://github.com/containers/buildah
Considering that some of our plugins use CRI-O runtime it could be
a good idea to get rid of docker as a builder. It should allow us
not to run docker daemon at all, even for build purposes.
Kubernetes also goes this way encouraging users to switch to CRI
runtimes (CRI-O and containerd), so having non-docker builds supported
looks good from this perspective too.
