Initialize variable.

--- plugins/node.d/multiping.in.orig	2018-12-19 20:56:49 UTC
+++ plugins/node.d/multiping.in
@@ -58,6 +58,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Bos
 host=${host:-www.google.com}
 
 
+site=0
 if [ "$1" = "config" ]; then
     echo graph_title Ping times
     echo 'graph_args --base 1000 -l 0'
