Flush output from timing script.

(cherry picked from commit 771768966f)

test/utils/shippable/timing.py

@@ -8,3 +8,4 @@ start = time.time()
 for line in sys.stdin:
     seconds = time.time() - start
     sys.stdout.write('%02d:%02d %s' % (seconds // 60, seconds % 60, line))
+    sys.stdout.flush()