My only reason for making a new attribute is that I am unsure if current users of the `compiletime` attribute want it to also update the cache. The functionality of the apt cookbook's `compiletime` attribute is [pretty specific](https://github.com/opscode-cookbooks/apt#attributes) and not necessarily part of what people want/need for running updates at compile time. As I discussed in my PR, I think this probably needs to be addressed by a larger refactor. This implementation adds the desired functionality without breaking anything for current users.