Minimize external dependencies on Linux

[stormshield-guillaumed]

This PR does not change the output, I checked it by running the CI on my branch. It would be great to minimize the use of external dependencies which are not necessary. The reason is on a system using SELinux, where you need a policy to allow the different actions of you program, the actual implementation on Linux makes you write a lot of rules to allow the execution of all the tools used. With the refactor, you only need to allow execution of hostnamectl and read access on both files.