Default path to controller config (gosdn.toml/development-gosdn.toml) is not working

Description

On develop the config file needs to be explicitly added as a parameter when starting the controller or it can't be found which leads to the controller not starting at all. Maybe we even want to use another file (e.g. development-gosdn.toml) during the development process.

Expected Behavior

It is possible to start the controller without explicictly adding the path to the config file when starting the controller.

Actual Behavior

Controller does not start without adding the path to the config file manually.

Steps to Reproduce

1. Pull develop.
2. Build and run gosdn.