This commit adds some recovery if Vagrant fails to reattach or clone a vmdk disk that needs to be resized. It first moves the original disk (after cloning) to a backup file. If something fails, it will reattach the original disk to the guest and continue to raise the exception.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.