Fixed PSU power consumption calculation

When PSUs were found, the voltage value was never set, raising an
exception when trying to multiply current * voltage (float * None).

This patch reads per PSU voltage (with 230V as default) and define power
consumption from it.

netbox_agent/power.py

@@ -105,18 +105,20 @@ class PowerSupply():
             return False
 
         # find power feeds for rack or dc
-        voltage = None
         pwr_feeds = None
         if self.netbox_server.rack:
             pwr_feeds = nb.dcim.power_feeds.filter(
                 rack=self.netbox_server.rack.id
             )
-        if pwr_feeds is None or not len(pwr_feeds):
+
+        if pwr_feeds:
+            voltage = [p['voltage'] for p in pwr_feeds]
+        else:
             logging.info('Could not find power feeds for Rack, defaulting value to 230')
-            voltage = 230
+            voltage = [230 for _ in nb_psu]
 
         for i, nb_psu in enumerate(nb_psus):
-            nb_psu.allocated_draw = float(psu_cons[i]) * voltage
+            nb_psu.allocated_draw = int(float(psu_cons[i]) * voltage[i])
             if nb_psu.allocated_draw < 1:
                 logging.info('PSU is not connected or in standby mode')
                 continue