Add System monitoring component

[fabaff]

Description:

This is a limited prototype/proposal for a system_monitoring component. As mentioned in #10118 should this help us to avoid the issue with the naming as the names are handled by the component through a dict lookup. Also, units of measurement and icons would be identical across platforms.

Depends on: #10555

Related issue (if applicable): fixes #10118

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

Example entry for configuration.yaml (if applicable):

system_monitoring:
  - platform: cpuspeed
  - platform: demo

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.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[MartinHjelmare]

I'd leave this not overwritten and also remove the value property, and let platforms overwrite state.

[fabaff]

It seems that my intention was not clear here and the current state of this PR is not reflecting this. Platforms should not longer need to take care about converting or rounding the data. The component will process or preparing the data which then are used for the state.

[houndci-bot]

module level import not at top of file

[balloob]

I'm not a fan of this approach. I don't see any benefit compared to the sensor component. If we want names and units to be consistent, can't we just have system monitoring platforms do that? (also, how many system platform monitoring components do we need?)

[fabaff]

We have system monitoring sensor platforms for that and we use them. With the introduction of this component we would have been capable to offload the whole conversion and round process from the platforms to the component. Also, it would have been possible for users set the unit of measurement according their needs.

also, how many system platform monitoring components do we need?

The more interesting questions is not how many platforms we need but how many we already have and can profit. The cpuspeed platform is boring as there is only the frequency of the chip which comes in Hz. The netdata platform is quite limited because of it's hard-coded entities and the systemmonitor has to perform calculations on some values.

I will not forget this and re-open it in 2018 when I spend more time thinking about additional benefits.