Tado: Initiate websession inside event loop

[balloob]

Description:

Fixes:

Error setting up platform legacy
Traceback (most recent call last):
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/device_tracker/setup.py", line 69, in async_setup_legacy
    self.platform.get_scanner, hass, {DOMAIN: self.config})
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/tado/device_tracker.py", line 33, in get_scanner
    scanner = TadoDeviceScanner(hass, config[DOMAIN])
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/tado/device_tracker.py", line 64, in __init__
    hass, cookie_jar=aiohttp.CookieJar(unsafe=True))
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/cookiejar.py", line 55, in __init__
    super().__init__(loop=loop)
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/abc.py", line 146, in __init__
    self._loop = get_running_loop(loop)
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/helpers.py", line 267, in get_running_loop
    loop = asyncio.get_event_loop()
  File "/usr/lib/python3.6/asyncio/events.py", line 694, in get_event_loop
    return get_event_loop_policy().get_event_loop()
  File "/usr/lib/python3.6/asyncio/events.py", line 602, in get_event_loop
    % threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'SyncWorker_18'.
Error setting up platform legacy
Traceback (most recent call last):
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/device_tracker/setup.py", line 69, in async_setup_legacy
    self.platform.get_scanner, hass, {DOMAIN: self.config})
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/tado/device_tracker.py", line 33, in get_scanner
    scanner = TadoDeviceScanner(hass, config[DOMAIN])
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/tado/device_tracker.py", line 64, in __init__
    hass, cookie_jar=aiohttp.CookieJar(unsafe=True))
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/cookiejar.py", line 55, in __init__
    super().__init__(loop=loop)
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/abc.py", line 146, in __init__
    self._loop = get_running_loop(loop)
  File "/srv/homeassistant/lib/python3.6/site-packages/aiohttp/helpers.py", line 267, in get_running_loop
    loop = asyncio.get_event_loop()
  File "/usr/lib/python3.6/asyncio/events.py", line 694, in get_event_loop
    return get_event_loop_policy().get_event_loop()
  File "/usr/lib/python3.6/asyncio/events.py", line 602, in get_event_loop
    % threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'SyncWorker_18'.

Related issue (if applicable): fixes https://community.home-assistant.io/t/0-94-smarthab-watson-tts-azure-event-hub/120228/15?u=balloob

Pull request with documentation for home-assistant.io (if applicable): home-assistant/home-assistant.io#<home-assistant.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

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

• The manifest file has all fields filled out correctly. Update and include derived files by running python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.