GitLab

* Added executils.Process helper

This helper should avoid common pitfalls arising mainly after the adoption
of the 'avrdude-stdin-hack'. For example see https://github.com/arduino/arduino-cli/pull/904
It also streamlines some of the most common operations (like process
Kill or Signal).

* Removed no more used executils.Command

* Run 'board list' test anyway

Even if no board are attached to the host system, it's always another
smoke-test that runs automatically.

Having this check enabled, for example, would have prevented:
https://github.com/arduino/arduino-cli/pull/904