installer: Don't run as root

There's many reason why it is and is going to
continue to be difficult to do this:

1. All display-managers (excluding slim) default PAM rules
   disallow root auto login.

2. We can't use wayland

3. We have to use system-wide pulseaudio

4. It could break applications in the session.
   This happened to dolphin in plasma5
   in the past.

This is a growing technical debt, let's just use
passwordless sudo.