setup.py: set the same env vars for testing as autotools
setup.py: set the same env vars for testing as autotools

Also don't print a Python stack trace of the calling process on
error, just return the error status.

GNOME/pygobject,pexip/pygobject,pexip/pygobject,pexip/pygobject,GNOME/pygobject,GNOME/pygobject