With recent docker versions, the build command allows specifying a non-default Dockerfile, allowing to store multiple docker builds on the same repository.

It would be great if there would be another field in the build step to provide the path for a non-default Dockerfile.

For example, this is useful when building a Ruby on Rails application that has a frontend and workers, that are running from the same code base with different requirements and different command lines.

Currently my workaround is when building a project into multiple images, before each docker build step I put in a shell build step that does `ln -sf path/to/real.Dockerfile Dockerfile`. This is not ideal.