[sensor/sma] SMA Solar Inverter sensor

[kellerza]

Description:
This is a sensor for an SMA solar inverter with WebConnect.

There are 4 predefined sensors, but new sensor keys can be added in the custom section. These values can found by inspecting the local web interface's traffic.

Currently tested on Sunnyboy 1.5 (should be ok for 2.5)

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#1668

Example entry for configuration.yaml (if applicable):

sensor sma:
  - platform: sma
    host: 192.168.88.199
    password: !secret sma_password
    group: installer
    sensors:
      current_consumption: [total_consumption]
      current_power: 
      total_yield: 
      some_new_sensor:
    custom:
      some_new_sensor:
        key: 6100_40263ZZZ
        unit: kW

Checklist:

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

• Documentation added/updated in home-assistant.github.io

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).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

[mention-bot]

@kellerza, thanks for your PR! By analyzing the history of the files in this pull request, we identified @balloob, @fabaff and @robbiet480 to be potential reviewers.

[kellerza]

@pvizeli this sensor need to close it's session on EVENT_HOMEASSISTANT_STOP. It uses async and the shared aiohttp session.

Unfortunately the session gets closed before the sensor gets time to send it's "logout" request. This raises the following exception

Any ideas how we can keep the session open until all components that rely on it successfully closes?

[pvizeli]

@kellerza create you own session without auto cleanup and cleanup self after close. See on helpers/aiohttp_client

[pvizeli]

I will change that the default session close with connector, so you code will work. I make a PR for that at morning.

[pvizeli]

Looks good. Only a short comment and I merge it.

[pvizeli]

We have a new helpers with timedelta support and now CONF_SCAN_INTERVAL is also a timedelta.