Add stripe-mock to storj up

[dlamarmorgan]

Use Stripe-Mock for easy integration testing. Stripe-Mock is stateless, if you want it to respond a certain way because of some state you would need to add that into the test.

Acceptance Criteria:

• write an integration test with stripe mock basically as a POC with storj/up.
  • this would mean that stripe-mock is now integrated with Storj/up and we would be able to send requests to stripe-mock and get the correct responses.