[sensors] Patch proposal: add sensors for cpu, disk and fans

[Davide Guerri]

Hi,
I added support for reading sensor data (where available) and exposing them via the API.

The API is exposed under the hardware section, so the API calls would look like:
 - https://{{hostname}}:8006/api2/json/nodes/{{node}}/hardware/sensors/temperature/disk/values
 - https://{{hostname}}:8006/api2/json/nodes/{{node}}/hardware/sensors/temperature/cpu/values
 - https://{{hostname}}:8006/api2/json/nodes/{{node}}/hardware/sensors/fan/speeds

The library needs some more testing on platforms other than Intel. Should you be interested/willing to help, please feel free to reach out to me. 

If everything makes sense, I can submit the patches in this ML:

Library https://github.com/dguerri/pve-common/commit/6a19bb03392ff94598e9efc76202fd1f60bd86b8
API: https://github.com/dguerri/pve-manager/commit/b152f153d98037c896430d6a131a28e496b30d4a

Thanks,
 Davide.