Tests: Try to make CTestTestTimeout more robust

Write to the timeout test log file before sleeping and flush to be sure
it is created.  Move the check that the after-sleep line is not written
out to the ctest script.  Rename the CheckChild test to TestSleep since
it no longer checks.  Do not try to read the log file if it does not
exist.
Merge topic 'revise-CTestTestTimeout' into next

9afcecaf Tests: Try to make CTestTestTimeout more robust