Update to python3, add error handling

When I ran this script, it failed because I didn't have python-lxml
installed. Newer Debian versions have removed many python2 packages, so
I also needed a python3 version of this. Upgrade the script to python3,
which ended up just being the file open mode :) At the same time, make
sure the fetch_artifact (which requires prodaccess) cannot fall through
by adding 'set -e' to the bash wrapper.

Change-Id: Ic8c7686722726fc937e1296313e039a0ebc24817
2 files changed