Prior to this commit, rsync-auto would not properly rsync realtive dirs
outside the cwd if defined in the Vagrantfile. This commit updates that
to ensure that the command looks at the Vagrant config to ensure that
folder was intended to be rsync'd to the machine even if outside the
current working dir.
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.