Comment 0 for bug 1771614

I was checking code for elements/ubuntu-core, specifically elements/ubuntu-core/root.d/10-cache-ubuntu-image, and was not able to understand why and when was it supposed to be used.

Defaults provided for various variables (e.g. https://github.com/openstack/diskimage-builder/blob/a8df61edbb6cec3e1e9861cfc7f6b92d80418ee9/diskimage_builder/elements/ubuntu-core/root.d/10-cache-ubuntu-image#L28) are no longer valid.

I would suppose to either
a) document in README usage example and fix scripts accordingly, or
b) remove elements/ubuntu-core completely

Thanks.