Use vagrant-wrapper which fixes the Vagrant / bundler integration issues

...and clean up the cruft in the Rakefile.

This is possible now since vagrant-wrapper works on windows too:
https://github.com/org-binbab/gem-vagrant-wrapper/pull/4
https://github.com/org-binbab/gem-vagrant-wrapper/pull/5
https://github.com/org-binbab/gem-vagrant-wrapper/pull/6

Thanks @btm and @binarybabel!