[Nut-upsdev] Fix broken systemd integration in the build system

[Stuart D Gathman]

Long ago, Nostradamus foresaw that on Apr 11, Michal Hlavinka would write:

> This is no longer true for Fedora. Since Fedora 17, there is no /bin nor 
> /sbin now. Everything got moved to /usr/(s)bin. They are symlinks to /usr... 
> for now.

In the /sbin world, I have been creating custom nut packages that put
all the drivers in /sbin/ups.  This reduces changes of name conflicts
on a driver, and has less clutter.  Other packages use /usr/libexec for
plugins and drivers.