Code review comment for lp://staging/~doanac/uci-engine/apt-mirror-support

Do we really want to do this as part of uci-engine? I think it would make more sense to bake it into the images, so juju could use it. Perhaps we need a small program to bake our images, given a base of a Canonistack daily? I also want to bake in git and the common packages to all of our components so apt-get install in a charm is a no-op for many cases.