Use invoke-rc.d interface in postinst maintainer script

Make sure we don't invoke services if that's unwanted.

debian/ngcp-www-admin.postinst

@@ -28,7 +28,11 @@ fi
 
 # reload perl and/or apache modules
 if [ -x /etc/init.d/apache2 ]; then
+  if [ -x "`which invoke-rc.d 2>/dev/null`" ]; then
+    invoke-rc.d apache2 restart || true
+  else
     /etc/init.d/apache2 restart || true
   fi
+fi
 
 exit 0