qt-testrunner.py should write a status file

A test might have PASSed all its testcases, but might still exit with != 0, i.e. fail, for example because of a crash in the destructor. qt-testrunner will detect that and re-run the full test executable. But such events should be logged.

So qt-testrunner should output a machine-readable log file, mentioning

• BEGIN
• What was tested
• How many re-runs
• (maybe intermediate results)
• Final outcome
• END

qt-testrunner should flush that file to disk frequently. If the END is missing one can assume a crash/cancellation or other irregular termination, outside of qt-testrunner's control.

The filename should be placed into COIN_CTEST_RESULTSDIR and it should be named uniquely, since qt-testrunner is being executed once for each test.