Create a failed refund when insufficient funds are in order escrow

[steveklabnik]

Since this was previously failing (#435) I'm not sure what's right.

Currently porting https://github.com/balanced/balanced-api/blob/revision1/scenarios/orders/create_refund.yml over to cucumber:

  Scenario: Create a failed refund when insufficient funds are in order escrow
    Given I have created an order
    And I have tokenized a card
    When I make a POST request to the link "cards.debits" with the body:
    """ 
      { 
        "order": "<%= @orders_id %>", 
        "amount": 1234
      }
    """

    And I have tokenized a bank account
    Then I make a POST request to the link "bank_accounts.credits" with the body:
    """
    {
        "order": "<%= @orders_id %>", 
        "amount": 1234
      }
    """

    When I make a POST request to the link "debits.refunds" of that debit
    Then I should get a 409 status code
    And the response is valid according to the "errors" schema
    And the fields on this error match:
    """
      {
         "category_code": "account-insufficient-funds"
       }     
    """  

Right now, the 409 is returning a 201 instead. Seems bad. :/

/cc @matthewfl