Fix coverage generation script

Description

Closes #616 (closed)

• The coverage script was allowing a silent failure of the build. Since some packages were still built, some coverage results were still generated, so there was no obvious error
• This modifies the script to fail on the first error
• I also decreased the verbosity of the lcov commands to make the logs easier to look at
  • stdout is now written to a file which will be uploaded as an artifact of the job, in case we need to debug something
• In the future we should consider using colcon lcov-result which wraps the lcov commands

Notes for Reviewer

• Check the coverage results to see that all expected packages are there: e.g. vehicle_interface

Checklist

• Documentation was updated