Test that a network namespace trumps a fallback namespace where they overlap.

Sanity check the presence of the fallback namespace, should get the fallback resource.
Getting a network namespace resource that exists on the server, should succeed.
Getting a network namespace resource that does not exist on the server, should get a 404.
Creating two iframes for an existing and non-existing page, one should say "hello" the other should 404.
- hello heard
- 404 detected
PASS