Add script to clean up outdated boxes.

vagrant doesn't have a way to clean up outdated boxes.  I have an
open issue (https://github.com/mitchellh/vagrant/issues/4412).
I will likely implement it once I get feedback from the maintainer
as to how he would want it exposed in the command-line UI.
Fix mapping of home directory

The mapping of the home directory to /home/vagrant/host needs
to use double quotes for variable expansion
Merge branch 'master' of github.com:chrisvire/vagrant-sil