Fix for scram handling

Author: christkv

lib/db.js

@@ -1028,9 +1028,13 @@ var Db = function(databaseName, topology, options) {
 
     // If classic auth delegate to auth command
     if(authMechanism == 'MONGODB-CR') {
-      topology.auth('mongocr', authdb, username, password, function(err, result) {
-        if(err) return handleCallback(callback, err, false);
-        _callback(null, true);
+      topology.auth('scram-sha-1', authdb, username, password, function(err, result) {
+        if(err == null && result == true) return _callback(null, true);
+
+        topology.auth('mongocr', authdb, username, password, function(err, result) {
+          if(err) return handleCallback(callback, err, false);
+          _callback(null, true);
+        });
       });
     } else if(authMechanism == 'PLAIN') {
       topology.auth('plain', authdb, username, password, function(err, result) {