Switch to python3 in all our scripts shebangs

bin/varnishtest/huffman_gen.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import re
 import sys

bin/varnishtest/witness.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # This script is in the public domain
 #

doc/sphinx/vtc-syntax.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2006-2016 Varnish Software AS
 # All rights reserved.

include/generate.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2006 Verdens Gang AS
 # Copyright (c) 2006-2015 Varnish Software AS

include/tbl/style.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Very basic style-checker for include/tbl files.
 

lib/libvarnishapi/generate.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #-
 # Copyright (c) 2006 Verdens Gang AS
 # Copyright (c) 2006-2015 Varnish Software AS

lib/libvcc/generate.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2006 Verdens Gang AS
 # Copyright (c) 2006-2015 Varnish Software AS

lib/libvcc/vmodtool.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2010-2016 Varnish Software
 # All rights reserved.

lib/libvcc/vsctool.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- encoding: utf-8 -*-
 #
 # Copyright (c) 2017 Varnish Software AS

tools/gcov_digest.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (c) 2017 Varnish Software AS
 # All rights reserved.

tools/include_wash.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 from __future__ import print_function