Mongo tests need to return exit code from M.Run()

[jasonrichardsmith]

The current Mongo tests don't return the Exit code because it uses testing.M. Run returns an exit code that must be used to exit the tests.

https://github.com/microservices-demo/user/blob/master/db/mongodb/mongodb_test.go#L37

[jasonrichardsmith]

This also means failing test here needs to be fixed https://github.com/microservices-demo/user/blob/master/db/mongodb/mongodb_test.go#L136