Code review comment for lp:~lotheac/lightdm/utmpx

I've committed the core of this patch with the following changes:
- Don't stop opening PAM sessions for the greeter - the PAM configuration might require to set something up in the session hooks for the greeter so we need to run those (and it is a session, just not a user session). The correct way to solve this is to make the greeter use a different PAM service so it can have different configuration.
- Remove the record when the session exits
- Minor layout changes