Always default to 'root' as a user_name if no variable has been set.
This can easily happen as not every role sets the variable and instead
we only set it once in the user role.
Another way to possibly go about it in the future would be to inject the
'user_name' into each role that needs it as one of that role's default
variables. If it is specified by the user somewhere it _should_
override those defaults, though I have to read up on the exact variable
precedence.
By setting the `desired_package_state` variable we can change if ansible
should only ensure that the packages exist on the system (`present`) or
that they are also updated to their latest version (`latest`).
