Add explicit default values to pytest command line options to prevent
issues when running tests with pytest's parallel execution where
options are not present on upper conftest, so they're just not set at all.
After tests end, an extra check if performed, looking into node logs.
By default, it only searches for critical errors and scans for coredumps.
If the test has the fixture `check_nodes_for_errors`, it will search for all errors.
Both checks can be ignored by setting `ignore_cores_log_patterns` and `ignore_log_patterns`.
If any of the above are found, the test will fail with an error.
Use universalasync library to make test.py async code compatible
with synchronous code of dtest/ccm
Also, copied unmodified error_example_test.py from dtest as an example.
Run the test in `dev` mode only.
