Repeated tests on same machine might pass when they should fail

[ca-scribner]

I haven't caused the break myself, but looking at this test I think because of the caching it is possible to break the fetching of remote schemas without breaking the test by:

• run the test when everything works on a schema url. schema file is cached locally in /tml/hash
• break the code that fetches remote schemas
• run the test again on the same url. This will hit the cached file and pass even though it can't fetch it

Some easy fixes I think would either be testing on the remote-fetching more directly, or adding a ignore_cache arg?