switch project-requirements-change to use python3

Update the version of python used to run the requirements-check script
as part of the python3-first goal.

Change-Id: Ifa21c3b3d55988c725e049733b227fa0ee22fbbd
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

playbooks/files/project-requirements-change.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 # Copyright (C) 2011 OpenStack, LLC.
 # Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
 # Copyright (c) 2013 OpenStack Foundation
@@ -98,6 +98,8 @@ def main():
     os.chdir(args.src_dir)
     reqdir = args.reqs
 
+    print(sys.version_info)
+
     if reqdir is None:
         if args.local:
             print('selecting default requirements directory for local mode')