prepare_veewee_iso script updates

- clean up shadow file, do all cleanup at the end so changes are still saved to output dmg
- include OS X build version in output filename
- update comments and usage (attrib, 10.7 AutoPartition TODO)
postinstall.sh split out into separate components, system ruby

- no rvm by default, so we can keep using system Ruby
- use hashicorp's puppet-bootstrap to install vendor Puppet .pkg
- use chef omnibus installer
- set hostname/computer name to 'vagrant-osx-10N'