Fix syntax in setup_horizon

This patch fixes syntax errors in setup_horizon.sh.

Change-Id: Iea507bdf65718ca2f4ed423d3c2ad77a61869547

labs/osbash/scripts/ubuntu/setup_horizon.sh

@@ -60,8 +60,8 @@ function check_apache_service {
     until service apache2 status | grep 'not running'; do
         sudo service apache2 stop
         sleep 10
-        i ++
-        if [ $i -gt 3]
+        i=$((i + 1))
+        if [ $i -gt 3 ]
         then
             break
         fi