Improve Vagrant setup

Use debian/contrib-jessie64 base box, install python-cryptography before
saltstack bootstrap.

Vagrantfile

@@ -2,11 +2,14 @@
 # vi: set ft=ruby :
 
 Vagrant.configure(2) do |config|
-  config.vm.box = "debian/jessie64"
+  config.vm.box = "debian/contrib-jessie64"
+
   config.vm.hostname = "gvafile.local"
   config.vm.network "private_network", ip: "172.16.3.4"
+
   config.vm.synced_folder "../gvasalt/states/", "/srv/salt/"
   config.vm.synced_folder "../gvasalt/pillar/", "/srv/pillar/"
+
   config.vm.provider "virtualbox" do |vb|
      # vb.gui = true
      vb.memory = "512"

salt/bootstrap.sh

@@ -1,5 +1,10 @@
 #!/bin/sh -
 
+echo "deb http://httpredir.debian.org/debian jessie-backports main" >/etc/apt/sources.list.d/backports.list
+
+apt-get update
+apt-get install -y -t jessie-backports python-cryptography
+
 # We just download the bootstrap script by default and execute that.
 if [ -x /usr/bin/fetch ]; then
     /usr/bin/fetch -o - https://raw.githubusercontent.com/saltstack/salt-bootstrap/stable/bootstrap-salt.sh | sh -s -- "$@"