A couple of errors here:
1. Your XML is not well-formed as it contains non-escaped '&' characters; these should be replaced with '&'
2. Your XML elements are in a namespace (see 'xmlns' attribute), but your E4X query is not. You need to define the namespace, for example
var vcloud = new Namespace("http://www.vmware.com/vcloud/v1.5");
and then the query will become
System.log("test 1 : " + xmldoc.vcloud::AdminVAppRecord.@name);
Hope this helps,
-Ilian