Validate initial_root_password, make sure it is >= 6 characters

Implemented according to @twk3 suggestion.

Through a pipeline of include and required. The include returns an empty string if the length is less than 6 characters which causes require to error.

I am surprised that they do not have such a behavior implemented natively and that we have to go such a hacky way but I guess it works so it's good

Closes: #200 (closed)