INFRA-3598: Don't use generic string error on 11600 error

Author: bozaro

auth.go

@@ -133,6 +133,9 @@ func (socket *mongoSocket) resetNonce() {
 		if result.Code == 13390 {
 			// mongos doesn't yet support auth (see http://j.mp/mongos-auth)
 			result.Nonce = "mongos"
+		} else if result.Code == 11600 {
+			socket.kill(errServerClosed, true)
+			return
 		} else if result.Nonce == "" {
 			var msg string
 			if result.Err != "" {
@@ -343,7 +346,7 @@ func (socket *mongoSocket) loginSASL(cred Credential) error {
 						server.close(true)
 					}
 					lock(false)
-					socket.kill(errors.New("server_shutdown: "+res.ErrMsg), true)
+					socket.kill(errServerClosed, true)
 				}
 				return fmt.Errorf("server returned error on SASL authentication step: %s", res.ErrMsg)
 			}

socket.go

@@ -769,7 +769,7 @@ func (socket *mongoSocket) readLoop() {
 					if socket.server != nil {
 						socket.server.close(true)
 					}
-					socket.kill(errors.New("server_shutdown: "+replyError.ErrMsg), true)
+					socket.kill(errServerClosed, true)
 					return
 				}