Add: Acceptance test for list expansion

This tests that a variable can contain the name of a list and it will
expand properly if that variable is double dereferenced.

"list" slist => { "1", "2", "3" };
"list_ref" string => "bundle.list";
$($(list_ref)) == $(list)
Merge pull request #2063 from nickanderson/redmine/6866

Add: Acceptance test for variable expansion