Fixed the problem that creation of ZooKeeper lib directory fails.

Change-Id: I50d423c03e3f7d031ed45a218c7e573348585a9e
diff --git a/onos.sh b/onos.sh
index beb874f..c3331de 100755
--- a/onos.sh
+++ b/onos.sh
@@ -230,7 +230,7 @@
   
   # Create the ZooKeeper lib directory
   if [ ! -d ${ZK_LIB_DIR} ]; then
-      local SUDO=${SUDO:-}
+      local SUDO=${SUDO:-sudo}
       local whoami=`whoami`
       {
           ${SUDO} mkdir ${ZK_LIB_DIR}