Start the service, catching and logging exceptions

def start(self, service):
        """
        Start the service, catching and logging exceptions
        """
        try:
            map(self.start_class, service.depends)
            if service.is_running():
                return
            if service in self.failed:
                log.warning("%s previously failed to start", service)
                return
            service.start()
        except Exception:
            log.exception("Unable to start service %s", service)
            self.failed.add(service)