Comment # 16 on bug 1198668 from Michal Suchanek

(In reply to Michal Koutn��� from comment #15)
> (In reply to Tejas Guruswamy from comment #14)
> > > systemctl show -p Before purge-kernels.service 
> > Before=shutdown.target YaST2-Second-Stage.service multi-user.target
> > YaST2-Firstboot.service
> 
> I'm not sure purge-kernels.service:Before=multi-user.target would cause the
> 'waiting for boot to finish' (actually is it a verbatim message? I can't
> grep it in sources). 

AFAICT it's /usr/lib/systemd/system/plymouth-quit-wait.service