Package too old for cleanbuild

[Michi Henning]

> Would it make sense to extend the snapcraft yaml to let the developer
> specify where build-packages and stage-packages should be taken from?
> 
> It would be nice to be able to run a "snapcraft cleanbuild" from zesty
> while effectively using all the packages from xenial+overlay... :-)

That certainly would be nice, yes. It would also be awesome to be able to point apt inside the container at my  apt-cacher-ng cache. As is, every failed attempt to do a cleanbuild downloads ~150 MB and, on a 3 Mbit link, takes 10-15 minutes. For development and debugging, we really need something like this. As is, it’s unbelievably painful.

Michi.