Use `vagrant --version` instead of Vagrant.require_version for now

It looks like Vagrant.require_version wasn't available early on. For
now we can just use `vagrant --version` to do the check. Later on we
can replace this with a proper Vagrant.require_version call.
i.e.) When we need to updated to 1.5.0 for Rsync support

Fixes: #147
Merge branch 'master' into issue-147