Terminate run.py without throwing tracebacks.

Pressing control-c while run.py is being executed has terminated the
script, but threw an ugly traceback. To signal the user that his
method of exit was appropriate, we handle control-c calling exit(0).

contrib_bots/run.py

@@ -5,6 +5,7 @@ import importlib
 import logging
 import optparse
 import os
+import signal
 import sys
 import time
 
@@ -16,6 +17,9 @@ if os.path.exists(os.path.join(our_dir, '../api/zulip')):
 
 from zulip import Client
 
+def exit_gracefully(signum, frame):
+    sys.exit(0)
+
 class RateLimit(object):
     def __init__(self, message_limit, interval_limit):
         self.message_limit = message_limit
@@ -147,4 +151,6 @@ def run():
     )
 
 if __name__ == '__main__':
+    original_sigint = signal.getsignal(signal.SIGINT)
+    signal.signal(signal.SIGINT, exit_gracefully)
     run()