Do not install SysV init-scripts on systemd-enabled hosts

Also, hint at example service unit files if systemd is detected. Thanks
to @mika for spotting a bug in the original iteration of this patch.

utils/install_server.sh

@@ -73,6 +73,16 @@ if [ "$(id -u)" -ne 0 ] ; then
 	exit 1
 fi
 
+#bail if this system is managed by systemd
+_pid_1_exe="$(readlink -f /proc/1/exe)"
+if [ "${_pid_1_exe##*/}" = systemd ]
+then
+	echo "This systems seems to use systemd."
+	echo "Please take a look at the provided example service unit files in this directory, and adapt and install them. Sorry!"
+	exit 1
+fi
+unset _pid_1_exe
+
 if ! echo $REDIS_PORT | egrep -q '^[0-9]+$' ; then
 	_MANUAL_EXECUTION=true
 	#Read the redis port