Improve log file post-processing in trigger tests
Changes are driven mainly by the need to see more detailed output in CI when a test fails. I applied the changes in the exec shell scripts in TrigUpgradeTest and TriggerTest.
Changes:
- print the athena command before execution (and not after) using bash debug mode
- merge the two log files in newJO test before post-processing
- re-apply !21762 (closed) which was closed by mistake and forgotten
- print the full athena log to stdout if athena fails in CI
- add some comments in post-exec scripts to separate the steps
Jira: ATR-19383