nixos/tests/chromium: Check new userns sandbox.

Since Chromium version 42, we have a new user namespaces sandbox in the
upstream project. It's more integrated so the chrome://sandbox

 page
reports it as "Namespace Sandbox" instead of SUID sandbox, which we were
re-using (or abusing?) in our patch.

So if either "SUID Sandbox" or "Namespace Sandbox" reports with "Yes",
it's fine on our side.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>