Add error handler
Add error handling to login.call

Because it should. And specifically so we can debug this test better,
which very very rarely fails:

  API
    Upgrading my account
      When Recurly can't find my account
        PUT /api/:user/subscription/change/large-ec2
Update api.coffee
Merge pull request #646 from scraperwiki/error-handling-to-delete-dataset

Add error handling to login.call in tests