sensor-mon: Watch for InterfacesAdded

Start handling the InterfacesAdded signal for the threshold interfaces.
This is so that if a sensor has a threshold alarm set, but then restarts
and then doesn't have it set, sensor-monitor will get the update to the
new good value.

Previously, sensor-monitor would still log a threshold alarm on every
power on after a sensor daemon restarted and then showed no alarm.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I691c8949165bc29ac2eab4190e5dc9a9283bd2e6
2 files changed