code: func VimValidateVirtualCenter(c *vim25.Client) error {
  	if c.ServiceContent.About.ApiType != "VirtualCenter" {
  		return errors.New(ErrVirtualCenterOnly)
  	}
  	return nil
  }
docs: // VimValidateVirtualCenter ensures that the client is connected to vCenter.
  //
  // This is a lower-level method that does not take the wrapped client from the
  // higher-level govmomi object, and can be used to facilitate validation when
  // it's not available.