FROM scratch dockerfiles, base images

[lachmanfrantisek]

• scratch does not need a tag.
• think about some exceptions for such Dockerfiles (or maybe also for base images).

[lachmanfrantisek]

@jscotka

[TomasTomecek]

exception +1
we should handle this somehow, but it's totally a corner case

[jscotka]

yep, exception is fine.