always use explicit python version at current stage.
Signed-off-by: Joe Guo <joeg@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Noel Power <npower@samba.org>
Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Thu Mar 7 13:03:56 UTC 2019 on sn-devel-144
-#!/usr/bin/python
+#!/usr/bin/env python3
#
# Simple subunit testrunner for python
# Copyright (C) Jelmer Vernooij <jelmer@samba.org> 2014