Live environment fixes & persistent storage

This PR makes the following changes:
- add packages for dropbear & btrfs support
- stop removing the time zone data
- get rid of the prompt on shutdown and reboot
- remove more unneeded files in the cleanup hook
- refactor includes to be more scalable
- use the right paths to remove kernel modules
- add the first minimal motd
- ACPI: make the shutdown button work
- add init script for Docker; handle symlinks for /var/lib/docker and for TMPDIR
- add persistent storage which handles both debian2docker and boot2docker labeled partitions