Fixes port type from argument parser. (GoogleCloudPlatform#1599)

Author: gguuss

iot/api-client/end_to_end_example/cloudiot_pubsub_example_mqtt_device.py

@@ -183,7 +183,7 @@ def parse_command_line_args():
         default='mqtt.googleapis.com',
         help='MQTT bridge hostname.')
     parser.add_argument(
-        '--mqtt_bridge_port', default=8883, help='MQTT bridge port.')
+        '--mqtt_bridge_port', type=int, default=8883, help='MQTT bridge port.')
     parser.add_argument(
         '--message_type', choices=('event', 'state'),
         default='event',