x/network/integration and x/mongo/driver/integration tests take in a -host flag which defaults to 127.0.0.1:27017. 

1. This default means tests will fail if the cluster you're testing against doesn't have a member on localhost:27017
2. It looks like this flag isn't being used

Removing this flag and setting the host from MONGODB_URI will give people more flexibility on how they run tests.