fix healthcheck CI test

[jchapma]

Issue Description
Some healthcheck CI tests are failing

Steps to Reproduce
sudo pytest -s -v ./dirsrvtests/tests/suites/healthcheck/healthcheck_test.py

Expected results
Tests should pass

Screenshots
FAILED dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_healthcheck_standalone
FAILED dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_healthcheck_standalone_tls
FAILED dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_healthcheck_replication
FAILED dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_healthcheck_replication_tls
FAILED dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_healthcheck_backend_missing_mapping_tree
ERROR dirsrvtests/tests/suites/healthcheck/healthcheck_test.py::test_lint_backend_implementation

[progier389]

FYI: I got the same issue while running test after backporting the lmdb fixes to 2.5 branch
And in fact healthcheck_test.py is not the only one being impacted healthcheck_config_test.py is also impacted.

I identified a first problem: by default the auditlog is not buffered and healthcheck issue a warning about it.
Guess we should not directly use topology_st but a
healthcheck_topology module fixture that ensure that the instance is properly configured to have no healthcheck warning by default.

should also improve run_healthcheck_and_flush_log to help the debbuging.
Typically by adding the expected result and the testcase name in the log:

•    log.info(f'Use healthcheck with --json option. Expecting {searched_code}. Testcase is {os.getenv("PYTEST_CURRENT_TEST")}.')
  

and also log a message if the result is None