Added /var/lib/apt/lists as a cached dir within the apt bucket

Hi,

I have made some small changes to allow vagrant-cachier to support provisioning a debian box while offline. This is particularly useful when developing on the train etc. Hopefully you will find this pull request useful.

According to [Wikipedia](http://en.wikipedia.org/wiki/Advanced_Packaging_Tool#Files) /var/lib/apt/lists is the "storage area for state information for each package resource specified in sources.list". I have added this directory to the cached directories in the apt bucket. This enables apt to install cached packages without hitting the remote repositories for the main package lists.