[atlas] Probe downtime notification

[Micha Bailey]

I got an email 20 minutes ago telling me that my probe (#25346) is down,
and apparently it's been down since 2016-01-24 15:11:10 UTC -- almost 24
hours. My settings are such that I should be getting an email within 15
minutes. Does anyone know why it's not emailing me right away? Has this
happened to anyone else?