Stop jhr XHR function from swallowing JSON.parse error

[silasdavis]

There are a number of circumstances where the server may return a non-empty non-JSON response:

• Connection refused
• Bad origin
• Failure to reverse proxy
• Other middleware

In these cases jhr dies silently and so the front end cannot easily display an error message. This change wraps the JSON parsing in a function with a try catch and returns an appropriate error.

I have an issue with the tests - the pass successfully in the browser (by loading runner.html) but they fail with yarn test which complains with Failed assertion: expected: [object Object], but was: [object Object]. This is different to failure in the browser UI that gives you a nice string diff between the objects. it seems like gulp-qunit is ending up with a different broken implementation of deepEqual. I tried upgrading gulp-qunit and qunit but it didn't help. Perhaps you have an idea how to fix, otherwise we can work around it some other way. It's odd because I don't see the difference between the other usages that work fine.

[cainlevy]

I think it's a legacy issue in PhantomJS. The console logger isn't as capable.

Speaking of PhantomJS issues -- the expected error is different, too:

HTTP response 'Origin is not a trusted host.' is not JSON as expected: SyntaxError: JSON Parse error: Unexpected identifier "Origin"