handle KeyboardInterrupt

When running zuul in non-daemon mode (with -d), it is often useful to
abort it using Control + C.

Change-Id: I385a41625633f3120b95c07283bef015824e5853
Reviewed-on: https://review.openstack.org/13571
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins

zuul-server

@@ -101,8 +101,11 @@ class Server(object):
         signal.signal(signal.SIGHUP, self.reconfigure_handler)
         signal.signal(signal.SIGUSR1, self.exit_handler)
         while True:
-            signal.pause()
-
+            try:
+                signal.pause()
+            except KeyboardInterrupt:
+                print "Ctrl + C: asking scheduler to exit nicely...\n"
+                self.exit_handler( signal.SIGINT, None )
 
 if __name__ == '__main__':
     server = Server()