Improve log file post-processing in TriggerTest
This is a cherry-pick of the second commit in !22535 (merged) which is relevant for release 21 (the first commit was relevant only for master).
Changes:
- print athena command before execution, not after
- print full log to stdout if athena fails in CI
- add comments in post-exec to separate the steps
Jira: ATR-19383
(cherry picked from commit a19f624b)