Change ordering of user lookup vs. password hashing (#5614)
Change ordering of user lookup vs. password hashing (#5614)

* Change ordering of user lookup vs. password hashing

This fixes a very minor information leak where someone could brute force
the existence of a username. It's not perfect as the underlying storage
plays a part but bcrypt's slowness puts that much more in the noise.

hartsock/vault,joelthompson/vault,kingland/vault,quixoten/vault,joelthompson/vault,hashicorp/vault,kingland/vault,hashicorp/vault,rnaveiras/vault,rnaveiras/vault,hartsock/vault,hashicorp/vault,rnaveiras/vault,hashicorp/vault,joelthompson/vault,hartsock/vault,quixoten/vault,rnaveiras/vault,quixoten/vault,hashicorp/vault,joelthompson/vault,kingland/vault,rnaveiras/vault,quixoten/vault,kingland/vault,kingland/vault,hartsock/vault,hartsock/vault,hashicorp/vault