DAD Disk Space Warnings

DAD exposes a function to check on the status of the drive that DAD itself is stored on. Using this we can very easily generate an alert. Since a disk space alert isn't based on any actual events, there's no need to populate the Events array in the genericAlert API:

used = Event.diskUtilization
if used > 98 then
  Alert.genericAlert(criticality: 5, description: "The log server is running out of disk space!  Utilization is currently #{used}%", short_description: "Disk space warning")
end