fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally

We now don't buffer anything inside runTestSuite, but the generating
process itself could buffer e.g. stdout. Tell it not to do so.

go/neo/t/nxd/runTestSuite

@@ -62,6 +62,11 @@ def main():
         # a test run for given name and revision has already been completed
         return
 
+    # make sure we get output from subprocesses without delay.
+    # go does not buffer stdout/stderr by default, but python does for stdout.
+    # tell python not to buffer anything.
+    os.environ['PYTHONUNBUFFERED'] = 'y'
+
     # run the tests
     devnull = open(os.devnull)
     while 1: