Upgrade paho-mqtt to 1.4.0

[fabaff]

Description:

Changelog: https://github.com/eclipse/paho.mqtt.python/blob/master/ChangeLog.txt

Example entry for configuration.yaml (if applicable):

mqtt:
  broker: localhost
  discovery: True

$ mosquitto_pub -h 127.0.0.1 -p 1883 -t "homeassistant/binary_sensor/garden/config" -m '{"name": "garden", "device_class": "motion"}'

2018-09-18 14:02:15 INFO (MainThread) [homeassistant.core] Bus:Handling <Event platform_discovered[L]: service=load_platform.binary_sensor, platform=mqtt, discovered=name=garden, device_class=motion, platform=mqtt, state_topic=homeassistant/binary_sensor/garden/state>
2018-09-18 14:02:15 INFO (MainThread) [homeassistant.components.binary_sensor] Setting up binary_sensor.mqtt
2018-09-18 14:02:15 INFO (MainThread) [homeassistant.core] Bus:Handling <Event state_changed[L]: entity_id=binary_sensor.garden, old_state=None, new_state=<state binary_sensor.garden=off; friendly_name=garden, device_class=motion @ 2018-09-18T14:02:15.523584+02:00>>

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable ([example][ex-requir]).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.

[balloob]

Oh, do you see in the changelog the better asyncio support? Even added an example.

https://github.com/joernheissler/paho.mqtt.python/blob/1a7ad0d638e63a51438dc32453e85ce0e1d87f2a/examples/loop_asyncio.py

We should switch our MQTT integration to that. CC @OttoWinter

[balloob]

Tracked issue for MQTT conversion to asyncio here: #16690

[fabaff]

I did see it but my "asyncio" coding skill are still limited.