WIP: windows builder provisioning

ref https://github.com/staticfloat/julia-buildbot/issues/3

Not fully ready yet, but in case you want to have a look at it

For now my Vagrantfile is pretty much just
```
Vagrant.configure("2") do |config|
  config.vm.box = "ferventcoder/win7pro-x64-nocm-lite"
  config.vm.communicator = "winrm" # important!
  config.vm.provision "shell", path: "support/choco_juliadev.ps1"
end
```
But I think to be proper about licenses we will need to figure out how to build our own vagrant boxes from authorized evaluation images.