Move from Veewee to Kiwi Image building

Kiwi is much faster and less error prone as Veewee but at the time Kiwi
didn't support Vagrant images which it now does.

This is just the basic step, the documentation needs to be updated and maybe some additional tests/error handling should be added.
This can be simplified to `tmp_dir = options[:kiwi_tmp_dir] || "/tmp/kiwi-vagrant-build-environment"`.

I would also use a simpler default name, but put `pennyworth` in it so that it's clear what created the directory. E.g. `/tmp/pennyworth-kiwi-builds`.