Update image_commands to match updates on base:

  fix call of ImageCommands, object should not be called, only class should be
  remove loopback_file reference, not existing anymore
  filesystem not available anymore, and depends on volume layout so remove the
  execute commands after the user_packages install, else user won't be able to
  call or update installed packages
Install packages after debootstrap because debootstrap does not support
all packages and fails at config time for a few. Closes #119

Packages are installed at system modification

install local packages after repo ones
use bootstrapper mirror for apt source