Vagrantfile: ensure vagrant-vbguest plugin is enabled
Vagrantfile: ensure vagrant-vbguest plugin is enabled

Issue: #98
Warn if the vagrant-vbguest is not enabled. New users wanting to
test out the vagrant box will be confused by the error message
of the vagrant machine not booting.

senior7515/smurf,senior7515/smurf,senior7515/smurf