Prior to this commit, when users invoked the `rsync-auto` command using the docker provider with boot2docker, vagrant would rsync all known containers using the boot2docker vm rather than the current working dir. This commit updates that behavior to ensure that only the current working dirs vagrant machines will be rsynced.
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.