Default to the first credential tab if no cookie

Also removes the credential dialog id, to ensure persistence across
sessions

static/js/directives/ui/credentials-dialog.js

@@ -34,7 +34,6 @@ angular.module('quay').directive('credentialsDialog', function () {
       }
 
       $rootScope.credentialsDialogCounter++;
-      $scope.dialogID = $rootScope.credentialsDialogCounter;
 
       $scope.hide = function() {
         $element.find('.modal').modal('hide');