当键未知时，解析ngFor中的嵌套JSON

 <select class="form-control selectpicker" data-style="form-control btn-primary" [(ngModel)]="serverName"  >
      <option  data-content="<i class='glyphicon glyphicon-cutlery'></i>" *ngFor="let instance of instances" [ngValue]="instance.insturl">{{instance.name}}</option>
    </select>
 <select class="form-control selectpicker" data