[9.18] chg: test: Improve pytest log output

[9.18] chg: test: Improve pytest log output

- increase clarity of multiline messages
- support `isc.query.*()` query&response logging
- replace use of `print()` statement with proper logging
- omit empty lines from test result output

Backport of MR !10590

Merge branch 'backport-nicki/improve-pytest-logging-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!10661