Update template contents owner tests to match spec changes

After https://github.com/w3c/html/commit/57c545df7d03f7afd60208fac35b907e3f2635cf, every template content DocumentFragment gets a new ownerDocument unless that template's ownerDocument was created for some other template (i.e., for another template in the same document or for a nested template).

See spec bug at https://www.w3.org/Bugs/Public/show_bug.cgi?id=23990 for more discussion of this change.