create /var/run/naemon in RPM for pid with systemd

In RPM, naemon is built to create its PID file in directory
/var/run/naemon. If the directory does not exist, naemon exits with
return code 254. On RC script based systems, naemon init script creates
this directory properly but systemd does not. With systemd, the RPM
should therefore create the directory itself.

Signed-off-by: Rémi Palancher <remi@rezib.org>