Add support for alternative discovery protocol (20002/udp) (#488)

This will broadcast the new discovery message on the new port and log any responses received as unsupported devices.

kasa/exceptions.py

@@ -3,3 +3,7 @@
 
 class SmartDeviceException(Exception):
     """Base exception for device errors."""
+
+
+class UnsupportedDeviceException(SmartDeviceException):
+    """Exception for trying to connect to unsupported devices."""