libhdfs++: Don't retry if there is an authentication failure

"Authentication failed" status falls into the general !status.ok() block in the HA retry policy so it will keep attempting to failover. If the client isn't kerberized, or doesn't have the right ticket it should give up and return a meaningful error message (right now it returns a generic bad connection failure string).

Wouldn't hurt to check the FixedDelayRetryPolicy to make sure that doesn't also keep attempting to retry in the same way. I suspect it does.