- the previous logic only allowed one flag to be mocked at a time because it kept recalling sinon.stub
- now it's possible to mock multiple flags with different settings as we always just add to the same stub
refs https://github.com/TryGhost/Team/issues/1338
This adds some initial scaffolding to make it easier to test Members with Stripe
- `mockStripe` method to disable the network, so we can use nock to intercept
Stripe API calls
- `setupStripe` method to be called _before_ getting an agent so that Stripe is
configured
- `getMembersAPIAgent` to get an agent for the Members frontend API
- Can now easily mock labs flags as enabled or disabled using mockManager
- Updated some bits of code that directly mocked labs
- Aside: improved error thrown when things go wrong booting Ghost
