Revert "Reworked the internals on installing packages without callbacks before volumes are set up."

This reverts commit 97a1eb6c8680e4c3066e7352625176d905b332c9.  I have to revert this because none
of the 'before :install_packages' callbacks are set up either, meaning any PPAs or apt repositories
needed to be set up via callbacks simply won't be by the time our non-callback :install_packages
is called.