I searched for random_str in the foundation.js of foundation version 6 but this function does not exist.
Also Foundation.utils is reported as undefined when doing:
console.log(Foundation.utils);
I have initialized foundation6 before with:
<script type="text/javascript">
$(function(){
$(document).foundation();
}); // end jquery
</script>
This isn't a bug, we simple changed the structure of our utils, removed quite a few things and added a few others. I would recommend checking out Foundation JS Utilities page on our docs to see what is available.