This fixes "frequency file /var/lib/ntp/ntp.drift.TEMP: Permission denied".
Creating a directory via StateDirectory makes that directory /var/lib/ntp owned by root:root.
However, when running ntpd we change to user ntp (see ntpFlags), so the process cannot
actually use that directory.
Actually creating a home directory for the user at that location solves that problem.
(cherry picked from commit 31942f20f4)