Improve check for systemd in a template for Fedora

The /usr/bin/systemd symlink has been removed from the systemd package in Fedora Rawhide.

- http://pkgs.fedoraproject.org/cgit/systemd.git/commit/?id=c3b79820c74b69289284bcbdf5f5ebc359feae3b

Therefore, the current template script fails to find systemd on such a host.

```
# lxc-create -n test -t fedora -- --release=19
Host CPE ID from /etc/os-release: cpe:/o:fedoraproject:fedora:20
Checking cache download in /usr/local/var/cache/lxc/fedora/x86_64/19/rootfs ...
...
sed: can't read /usr/local/var/lib/lxc/test/rootfs/etc/rc.sysinit: No such file or directory
sed: can't read /usr/local/var/lib/lxc/test/rootfs/etc/rc.d/rc.sysinit: No such file or directory
sed: can't read /usr/local/var/lib/lxc/test/rootfs/etc/rc.sysinit: No such file or directory
sed: can't read /usr/local/var/lib/lxc/test/rootfs/etc/rc.d/rc.sysinit: No such file or directory
error reading information on service udev-post: No such file or directory
container rootfs and config created
```

I've created a patch to fix this problem.