fix wait-ready script

As noticed by @bflad, a successful last iteration would result in failure status.
Fixed now.

templates/default/systemd/docker-wait-ready.erb

@@ -1,9 +1,9 @@
 #!/usr/bin/env bash
 i=0
 while [ $i -lt <%= @service_timeout * 2 %> ]; do
-  ((i++))
   <%= @docker_cmd %> ps | head -n 1 | grep ^CONTAINER > /dev/null 2>&1
   [ $? -eq 0 ] && break
+  ((i++))
   sleep 0.5
 done
 [ $i -eq <%= @service_timeout * 2 %> ] && exit 1