[9.20] chg: test: Improve logging from isctest.run.retry_with_timeout

[9.20] chg: test: Improve logging from isctest.run.retry_with_timeout

Allow use of exception (and by extension, assert statements) in the
called function in order to extract essential debug information about
the type of failure that was encountered.

In case the called function fails to succeed on the last retry and
raised an exception, log it as error and set it as the assert message to
propagate it through the pytest framework.

Closes #5324

Backport of MR !10580

Merge branch 'backport-5324-pytest-isctest-run-logging-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10605