Fix failure when setting basic_users state: absent

[sjpb]

At some point loginctl format changed to include extra fields, some of which may be empty. Luckily we only care about the first two so don't have to parse this properly.

[rocky@demo-login-0 ~]$ loginctl list-sessions
SESSION  UID USER  SEAT TTY   IDLE SINCE
   1789 1000 rocky      pts/0 no        
   1796 1000 rocky      n/a   no        
   1797 1006 lab0       pts/1 no  

[sd109]

LGTM

[m-bull]

This works as-is, so I don't see the point in fussing about the methodology, though I've a minor comment on the use of JSON.

Approved, but also happy to re-review if you want to update to address the comment.