vagrant: Use rsync backend for file sharing

Vagrant defaults to nfs on linux, which requires root rights and changes
nfs configuration. The rsync backend is much less invasive, but needs
manual triggering (at least `vagrant rsync-auto`).

Closes #29

Vagrantfile

@@ -7,7 +7,7 @@ Vagrant.configure(2) do |config|
     end
 
     config.vm.synced_folder ".", "/vagrant", disabled: true
-    config.vm.synced_folder "dist/", "/usr/local/share/cockpit/" + File.basename(Dir.pwd), create: true
+    config.vm.synced_folder "dist/", "/usr/local/share/cockpit/" + File.basename(Dir.pwd), type: "rsync", create: true
 
     config.vm.provider "libvirt" do |libvirt|
         libvirt.memory = 1024