use print_function future
This uses from __future__ import print_function from "unrestricted" python code.
For restricted python in python scripts, this expects SlapOS to have slapos!1536 (merged) . Running ERP5 with this patch on an old SlapOS software release should probably be OK, especially because after all we don't have so much critical code using print.
To ease migration of custom project code, PythonCodeUtils was modified so that when running CodingStyle python scripts are checked with print_function future enabled.