fix bug when getting default VTRService
fix bug when getting default VTRService

cboling/xos,opencord/xos,zdw/xos,zdw/xos,zdw/xos,cboling/xos,opencord/xos,zdw/xos,cboling/xos,open-cloud/xos,open-cloud/xos,opencord/xos,open-cloud/xos,cboling/xos,cboling/xos