Restarts/reboots on the sensor side need to be accounted for on the backend

[bklaas]

If either the sensor service restarts or the device reboots (power outage, windows being windows, etc.), the ephemeral DB on the Sensor process is wiped and the data for that day when posted at midnight is going to not reflect the entire 24hrs of data.

We should at least account for this on the database side, possibly by shipping uptime/boot time to the backend so it can detect when we aren't sending a full 24h window of data.