Add generic script alarm.

# sla-contract-create GENERIC_SCRIPT_ALARM 1 evacuate

This alarm is a dummy one that just create the record in the DB, so external systems can
just trigger the alarm by following the documented callback

 PUT http://service:port/v1/sla/alarming?state=alarm&contract_id=XXXX&source=custom
or
 PUT http://service:port/v1/sla/alarming?state=alarm&source=custom
     body: {"alarm_id": "the_alarm_id"}