Direct all test output in the test runner to stderr because that's where...

Direct all test output in the test runner to stderr because that's where unittest is writing it, and it gives better ordering on Windows to not mix stdout and stderr.

runtests.py

 #!/usr/bin/env python
 
+from __future__ import print_function
+
 import atexit
 import os
 import sys
@@ -69,7 +71,7 @@ except ImportError:
     class SkipTest(Exception):  # don't raise, only provided to allow except-ing it!
         pass
     def skip_test(reason):
-        print("Skipping test: %s" % reason)
+        sys.stderr.write("Skipping test: %s\n" % reason)
 else:
     def skip_test(reason):
         raise SkipTest(reason)
@@ -1664,9 +1666,8 @@ class EndToEndTest(unittest.TestCase):
             out, err = p.communicate()
             res = p.returncode
             if res != 0:
-                print(command)
-                print(self._try_decode(out))
-                print(self._try_decode(err))
+                sys.stderr.write("%s\n%s\n%s\n" % (
+                    command, self._try_decode(out), self._try_decode(err)))
             self.assertEqual(0, res, "non-zero exit status")
         self.success = True
 
@@ -2049,21 +2050,22 @@ def main():
             for shard_num, return_code in pool.imap_unordered(runtests_callback, tasks):
                 if return_code != 0:
                     errors.append(shard_num)
-                    print("FAILED (%s/%s)" % (shard_num, options.shard_count))
-                print("ALL DONE (%s/%s)" % (shard_num, options.shard_count))
+                    sys.stderr.write("FAILED (%s/%s)\n" % (shard_num, options.shard_count))
+                sys.stderr.write("ALL DONE (%s/%s)\n" % (shard_num, options.shard_count))
         pool.close()
         pool.join()
         total_time = time.time() - total_time
-        print("Sharded tests run in %d seconds (%.1f minutes)" % (round(total_time), total_time / 60.))
+        sys.stderr.write("Sharded tests run in %d seconds (%.1f minutes)\n" % (round(total_time), total_time / 60.))
         if errors:
-            print("Errors for shards %s" % ", ".join([str(e) for e in errors]))
+            sys.stderr.write("Errors for shards %s\n" % ", ".join([str(e) for e in errors]))
             return_code = 1
         else:
             return_code = 0
     else:
         with time_stamper_thread():
             _, return_code = runtests(options, cmd_args, coverage)
-    print("ALL DONE")
+    sys.stderr.write("ALL DONE\n")
+    sys.stderr.flush()
 
     try:
         check_thread_termination(ignore_seen=False)
@@ -2091,6 +2093,7 @@ def time_stamper_thread(interval=10):
 
     interval = _xrange(interval * 4)
     now = datetime.now
+    write = sys.stderr.write
     stop = False
 
     def time_stamper():
@@ -2099,7 +2102,7 @@ def time_stamper_thread(interval=10):
                 if stop:
                     return
                 sleep(1./4)
-            print('\n#### %s' % now())
+            write('\n#### %s\n' % now())
 
     thread = threading.Thread(target=time_stamper)
     thread.start()