Add tests to the cmd line and env variables usage

[arbulu89]

After suffering a quite tricky issue: #409

The cobra/viper combination is super interesting to attach command lines flags and configuration files to variables, but it has the risk that it includes a high degree of auto-magic (black-box operations).

In order to deal with this, we would need to start adding tests to the command line and environment variables loading. Basically we need to know that all existing variables are used properly, if they are loaded of course.
This would help us a lot to avoid regressions.

Besides this, tests on the LoadConfig functions would be interesting too.