Prior to this commit, if you ran Vagrant in a different current working directory other than where a current guest machines location is, the file provisioner would not take into account the machines local dir, and would instead use the path where Vagrant was invoked to expand the `source` path option for a file provisioner. This commit fixes that by passing the root path `machine.env.cwd` when expanding the source dir.
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.