This commit updates how the virtualbox provider obtains `all_disks`. Instead of using the `list_hdds` driver method, which lists al known harddisks for an entire VirtualBox installation, it instead uses that array of disks to filter out the proper disks associated with the guest, given its existance inside the guests controller attachments.
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.