Libvirt provider

Adding Packer Qemu builder:
* Packer/answer_files/*_virtio: Install the virtio drivers from the ISO (NOT provided)
* windows_*.json needs some manual tweaks to match the virtio drivers ISO path

Adding Vagrant-libvirt provider:
* Uses the QEMU qcow2 images provided by packer to build the DetectionLab
* Vagrantfile needs manual tweaking to match libvirt's host configuration (backing store, network interfaces, etc)

README:
* Added separate README with instructions for libvirt

Packer/windows_2016.json

@@ -1,5 +1,48 @@
 {
   "builders": [
+    {
+      "type": "qemu",
+      "vm_name":"windows_10",
+      "communicator": "winrm",
+      "iso_url": "{{user `iso_url`}}",
+      "iso_checksum_type": "{{user `iso_checksum_type`}}",
+      "iso_checksum": "{{user `iso_checksum`}}",
+      "headless": false,
+      "boot_wait": "6m",
+      "boot_command": "",
+      "winrm_username": "vagrant",
+      "winrm_password": "vagrant",
+      "winrm_timeout": "4h",
+      "shutdown_command": "shutdown /s /t 10 /f /d p:4:1 /c \"Packer Shutdown\"",
+
+      "cpus": "2",
+      "memory": "2048",
+      "accelerator": "kvm",
+      "disk_size": "{{user `disk_size`}}",
+
+      "output_directory": "{{ user `packer_build_dir`}}",
+
+      "qemuargs": [
+        [ "-drive", "file={{ user `virtio_win_iso` }},media=cdrom,index=3" ],
+	[ "-drive", "file={{ user `packer_build_dir`}}/{{ .Name }},if=virtio,cache=writeback,discard=ignore,format=qcow2,index=1" ]
+	],
+
+      "floppy_files": [
+        "{{user `autounattend_virtio`}}",
+        "./floppy/WindowsPowershell.lnk",
+        "./floppy/PinTo10.exe",
+        "./scripts/fixnetwork.ps1",
+        "./scripts/MakeWindows10GreatAgain.ps1",
+        "./scripts/MakeWindows10GreatAgain.reg",
+        "./scripts/rearm-windows.ps1",
+        "./scripts/disable-screensaver.ps1",
+        "./scripts/disable-winrm.ps1",
+        "./scripts/enable-winrm.ps1",
+        "./scripts/microsoft-updates.bat",
+        "./scripts/win-updates.ps1"
+      ]
+
+	  },
     {
       "vm_name":"WindowsServer2016",
       "type": "vmware-iso",