Use 'hass.data' instead of global

[fabaff]

Description:

Use 'hass.data' instead of global and don't call update() in constructor..

Example entry for configuration.yaml (if applicable):

digital_ocean:
  access_token: !secret do_token

binary_sensor:
  - platform: digital_ocean
    droplets:
      - 'fedora-512mb-nyc3-01'

switch:
  - platform: digital_ocean
    droplets:
      - 'fedora-512mb-nyc3-01'

Checklist:

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

[mention-bot]

@fabaff, thanks for your PR! By analyzing the history of the files in this pull request, we identified @armills to be a potential reviewer.

[pvizeli]

You should not use DOMAIN for hass.data or if you import DOMAIN into a other namespace as platform rename to ... DOMAIN AS XY_DOMAIN. Otherwise it overwrite the domain of component from other platofrm. That is the reason for DATA_XY constante they easy to Import into other namespace.

[fabaff]

Using hass.data[DOMAIN] and importing DOMAIN on the platform-level seems to be pretty much how a bunch of components/platforms works. I don't understand why DOMAIN should overwrite the value of another platforms. Isn't the scope preventing this and if that happens wouldn't we see side effects from this?

I guess that prefixing the entries with DATA_ make sense.