We frequently get bugs like https://crbug.com/775061 which show that developers and sheriffs think a builder is out of space when it's really the build image running out of space.

This type of failure is about to get a lot more common as ChromeOS image reach the 2G hard limit.

We should start showing the real cause of the failure more clearly to make this easier to understand.

Perhaps raise a special exception when build_image or the mod_image_for_* scripts fail and add a waterfall note that points out the failures are on the image, not the builder? Something.