Ignore KeyError on delete of missing sensor

The duplicate sensor code can result in an id that never
gets added.  As such, do not worry if trying to delete
something that is already not there.

Change-Id: I77af1054097d4225ad8bff68a046c6ed28791e9b

pyghmi/ipmi/sdr.py

@@ -693,7 +693,10 @@ class SDR(object):
                 raise exc.BmcErrorException("Incorrect SDR record id from BMC")
             recid = newrecid
         for sid in self.broken_sensor_ids:
-            del self.sensors[sid]
+            try:
+                del self.sensors[sid]
+            except KeyError:
+                pass
 
     def get_sensor_numbers(self):
         return self.sensors.iterkeys()