coriolisenv.py fails to identify shell if run from a script

https://bugs.libre-soc.org/show_bug.cgi?id=714

whichCommand = subprocess.Popen ( ['which', shell ], stdout=subprocess.PIPE )

unfortunately, "shell" is of course the command - argv[0])

which, of course, when run from a script, is not /bin/bash, it's the name of the script.