Make the "tcp" system test fail if the Python tool used for establishing
TCP connections (ans6) logs a result different than "OK" after
processing a command sent to it (as that means the tool was unable to
successfully perform the requested action), with the exception of
cleanup errors at the end of the test which can be safely ignored. Note
that the tool not returning any result at all in 10 seconds is still a
fatal error in all cases.
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