vagrant: Add support for vagrant-libvirt

This change adds support for libvirt provider. Please note that libvirt
doesn't support the "virtualbox" mount type, so an another MOUNT_TYPE
has to be provided while using libvirt. 9p works well.

Signed-off-by: Michal Rostecki <mrostecki@opensuse.org>

Vagrantfile

@@ -33,6 +33,10 @@ Vagrant.configure("2") do |config|
     v.memory = NODE_MEMORY
     v.customize ["modifyvm", :id, "--audio", "none"]
   end
+  config.vm.provider "libvirt" do |v|
+    v.cpus = NODE_CPUS
+    v.memory = NODE_MEMORY
+  end
   if Vagrant.has_plugin?("vagrant-timezone")
     config.timezone.value = :host
   end