Empty array fix for xml

Currently when a parent_node contains no children the xml parser return child as nil

For ex: `<?xml version="1.0" encoding="UTF-8"?>
<ssh_keys>
 <ssh_key>   
 <links>     
 <link rel="self" href="/api/clouds/2/ssh_keys/8FA8RQF2MRS1C"/>     
 <link rel="cloud" href="/api/clouds/2"/>    
</links>
  <actions>
</actions>
<resource_uid>rightscale_test_eu</resource_uid> 
</ssh_key>
</ssh_keys>`
is parsed as
[{"links"=>[{"rel"=>"self", "href"=>"/api/clouds/2/ssh_keys/8FA8RQF2MRS1C"}, {"rel"=>"cloud", "href"=>"/api/clouds/2"}], "actions"=>nil, "resource_uid"=>"rightscale_test_eu"}]
notice "actions"=> nil doesn't match json as json returns "actions"=> []