Cause test to fail if any step fails

Without this change, a successfully generated menu in a previous test run could still exist after making changes. The verify_menu_config step in test_HLTmenu.sh would then pick up the old menu and pass, causing the test as a whole to pass even if there was an exception whilst generating the menu.

This shouldn't make any difference in the CI as it starts with a clean directory, but could give incorrect results when working locally.