This adds two new optional build steps. The first user of these is the
vagrant images but many of the targets can be simplified now.
- fs_hook: Anything that needs to happen before unmounting the image.
This happens after the OEM is installed but before disk images are
made. It can be used to copy any data out of the image.
- bundle_format: Many VM types ship as some sort of archive format
rather than plain disk images as this script originally assumed.
Adding this final step lets us stop using the conf step awkwardly.
Vagrant now ships with a Vagrantfile and related code included in the
OEM package. This lets us version our vagrant-side code along with the
images themselves as well making the coreos-vagrant repo optional again.
The coreos-vagrant code will still be useful for handling the fancier
cluster configuration stuff but no longer has to carry the plugin code.
