Add set -eux

This script should be set -e. Also added -ux for good measure. On RHEL,
os-refresh-config was failing to run due to a missing requirements.txt line on
argparse (separate patch), however the failure was not failing the image build
b/c this script was not -e.

Change-Id: Id36d61442d8104cada8346f47e63858cf7f08096
Merge "Add set -eux"