Really fix package initial installation when PID1 is systemd (Closes: #747863)

debian/nut-server.postinst

@@ -1,5 +1,18 @@
 #!/bin/sh -e
 
+handle_start_failure () {
+# The nut server part (upsd) must run in all cases except when MODE in
+# /etc/nut/nut.conf is set to "none", not set at all or if the machine is a
+# client.
+  [ -r /etc/nut/nut.conf ] && . /etc/nut/nut.conf
+  if [ -d /run/systemd/system ] \
+	  && [ "$MODE" = "none" -o "$MODE" = "netclient" -o -z "$MODE" ]; then
+    return 0
+  else
+    return 1
+  fi
+}
+
 case "$1" in
 
   configure)