When an image and features is defined, additional build options are not allowed

Hello all

I found out that defining an `image` and also `features` allows to build a new image with the desired features.
Unfortunately, it is not allowed to have `image` and `build` at the same time. I need `build.options` to pass additional parameters (`add-host`) to the docker command that is used to add the feature to the original image.

The only workaround right now is to create a Dockerfile with just the image as the `FROM` and then use `build` with the Dockerfile and not the image at all. Would be nice to be able to pass options when building an image with features as well instead of only when using a Dockerfile.