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

appengine/swarming/swarming_bot/bot_code/common.py

-# Copyright 2015 The Swarming Authors. All rights reserved.
+# Copyright 2015 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.
 
 """Utilities."""
 
 import logging
 import os
 import signal
 import sys
 
@@ skipping 24 matching lines @@
       proc.send_signal(signal.SIGTERM)
 
     sig = signal.SIGBREAK if sys.platform == 'win32' else signal.SIGTERM
     with subprocess42.set_signal_handler([sig], handler):
       proc.wait()
       return proc.returncode
   except Exception as e:
     logging.exception('failed to start: %s', e)
     # Swallow the exception.
     return 1