tools: Fix warnings reported by PyLint 2.6.0

"tools/weather_station.py:105: [W0707(raise-missing-from), UdpReceiverThread.initialize]
    Consider explicitly re-raising using the 'from' keyword"
"tools/weather_station.py:125: [W0707(raise-missing-from), SerialReceiverThread.initialize]
    Consider explicitly re-raising using the 'from' keyword"
"tools/weather_station.py:133: [W0707(raise-missing-from), SerialReceiverThread.receive]
    Consider explicitly re-raising using the 'from' keyword"

tools/weather_station.py

@@ -102,7 +102,7 @@ def initialize(self):
             self._connection.settimeout(3)
         except socket.error as err:
             self._connection = None
-            raise IOError(err)
+            raise IOError from err
 
     def receive(self):
         try:
@@ -122,15 +122,15 @@ def initialize(self):
         try:
             self._connection = serial.Serial(self._port, 9600, timeout=3)
         except serial.serialutil.SerialException as err:
-            raise IOError(err)
+            raise IOError from err
 
     def receive(self):
         try:
             self.handle_received(self._port, self._connection.readline())
         except serial.serialutil.SerialException as err:
             self._connection.close()
             self._connection = None
-            raise IOError(err)
+            raise IOError from err
 
 
 class RoomMapping():