Flush output right after printing running test name
If test program output on stderr (which is unbuffered), the output of the test program will appear before output from nxdtest advertising the program that is about to be executed, because nxdtest stdout is buffered (testnode does not set PYTHONUNBUFFERED, and eventhough nxdtest sets PYTHONUNBUFFERED in its own environ, this only applies to sub processes)