Cannot use vcgencmd in HassOS

[denics]

Stop using native rpi vcgencmd in favor of a more universal cat

Proposed change

SenseHAT integration code still rely on vcgencmd to read CPU temperature. However this is unavailable in HassOS and breaks the integration. The more universal cat /sys/class/thermal/thermal_zone0/temp read the temperature in all RPi OSs.

If this PR is merged, a little change should be done to the example in the documentation, as I show here.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml
  - platform: sensehat
    display_options:
      - temperature
      - humidity
      - pressure
  - platform: template
    sensors:
      sensehat_temperature:
        value_template: '{{ states("sensor.temperature") | round(1) }}'
        unit_of_measurement: '°C'
      sensehat_pressure:
        value_template: '{{ states("sensor.pressure") | round(1) }}'
        unit_of_measurement: 'mb'
      sensehat_humidity:
        value_template: '{{ states("sensor.humidity") | round(1) }}'
        unit_of_measurement: '%'

Additional information

• This PR fixes or closes issue: fixes Sense Hat does not work on HassOS #42708
• This PR is related to issue: NA
• Link to documentation pull request: NA, but willing to add the example as soon as this is accepted.

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

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

• Documentation added/updated for www.home-assistant.io

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

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

The integration reached or maintains the following Integration Quality Scale:

• No score or internal
• 🥈 Silver
• 🥇 Gold
• 🏆 Platinum

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.