Add box name

This is an improvement upon the original [PR #460](https://github.com/Varying-Vagrant-Vagrants/VVV/pull/460)

This now uses the current directory name for the box name, and this allows you to effectively configure the box name without actually configuring it.
Somehow this line does not exist in the VVV master. I don't know why but it needs to be in the PR (patch) to not break the vagrant provision.
Just see if you can fix that.