add support for "ok" as "normal" severity
add support for "ok" as "normal" severity

skob/alerta,0312birdzhang/alerta,mrkeng/alerta,skob/alerta,mrkeng/alerta,guardian/alerta,guardian/alerta,0312birdzhang/alerta,mrkeng/alerta,guardian/alerta,skob/alerta,guardian/alerta,skob/alerta,mrkeng/alerta,0312birdzhang/alerta