added sla for notifu

  * added custom variable sla in senu_check to use Sensu notification REST API handler
  * https://github.com/blufor/notifu#readme
Merge branch 'notifu_notification' of github.com:bogue1979/sensu-puppet into notifu_notification
Merge pull request #72 from bogue1979/notifu_notification

Notifu notification
Merge git://github.com/sensu/sensu-puppet