in post install script pick the right username when multiple users are logged in

Kevin was getting:
root              565   0.0  0.0  2601064   2308   ??  Ss   Thu02PM   0:01.12 /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow console
kevin             438   0.0  0.1  2633700   6500   ??  Ss   Thu02PM   0:07.64 /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow

I simulated this situation on my machine:
testuser        4982   0.0  0.2  2762304  32436   ??  Ss    6:08PM   0:01.34 /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow
darwin            65   0.0  0.2  2703164  28020   ??  Ss    1:29PM   0:07.32 /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow console