Logging system test backoff failures during teardown

[tseaver]

Similar to #5303, but this failure is in trying to delete the python logger during teardown:

tests/system/test_system.py::TestLogging::test_log_handler_async _has_entries. Trying again in 1 seconds...
_has_entries. Trying again in 2 seconds...
_has_entries. Trying again in 4 seconds...
_has_entries. Trying again in 8 seconds...
404 Log python does not exist, Trying again in 1 seconds...
404 Log python does not exist, Trying again in 2 seconds...
404 Log python does not exist, Trying again in 4 seconds...
404 Log python does not exist, Trying again in 8 seconds...
404 Log python does not exist, Trying again in 16 seconds...
404 Log python does not exist, Trying again in 32 seconds...
404 Log python does not exist, Trying again in 64 seconds...
404 Log python does not exist, Trying again in 128 seconds...
404 Log python does not exist, Trying again in 256 seconds...
FAILED
tests/system/test_system.py::TestLogging::test_log_handler_async ERROR

Might be due to overlapping test runs?