Fix shebang for htcondor make-jobfeatures

Without this patch, running the script from custom Python environments could fail. It has been seen in cases where users redefine the PYTHONHOME environment variable for their jobs.

This patch makes sure that the python version used is the appropriate according to the environment.

make-jobfeatures.htcondor

-#!/usr/bin/python
+#!/bin/env python
 #
 #  make-jobfeatures script for Machine/Job Features on HTCondor
 #