handle KeyboardInterrupt
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 <37c07a49ee3d5191376d758eb1d8298b34456b8e@inaugust.com>
Reviewed-by: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Approved: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Tested-by: Jenkins

gooddata/zuul,wikimedia/integration-zuul,devdattakulkarni/zuul_messaging,gooddata/zuul,wikimedia/integration-zuul,wikimedia/integration-zuul,devdattakulkarni/zuul_messaging,wikimedia/integration-zuul,gooddata/zuul,devdattakulkarni/zuul_messaging,gooddata/zuul,gooddata/zuul