Update copyright notice from Swarming to LUCI; add AUTHORS and CONTRIBUTORS.

client/utils/subprocess42.py

-# Copyright 2013 The Swarming Authors. All rights reserved.
-# Use of this source code is governed under the Apache License, Version 2.0 that
-# can be found in the LICENSE file.
+# Copyright 2013 The LUCI Authors. All rights reserved.
+# Use of this source code is governed by the Apache v2.0 license that can be
+# found in the LICENSE file.
 
 """subprocess42 is the answer to life the universe and everything.
 
 It has the particularity of having a Popen implementation that can yield output
 as it is produced while implementing a timeout and NOT requiring the use of
 worker threads.
 
 Example:
   Wait for a child process with a timeout, send SIGTERM, wait a grace period
   then send SIGKILL:
@@ skipping 568 matching lines @@
   """Runs an executable; kill it in case of timeout."""
   proc = Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, **kwargs)
   try:
     out, err = proc.communicate(timeout=timeout)
   except TimeoutExpired as e:
     out = e.output
     err = e.stderr
     proc.kill()
     proc.wait()
   return out, err, proc.returncode, proc.duration()