code: func (d *Daemon) ExecExists(name string) (bool, error) {
  	if _, err := d.getExecConfig(name); err != nil {
  		return false, err
  	}
  	return true, nil
  }
docs: // ExecExists looks up the exec instance and returns a bool if it exists or not.
  // It will also return the error produced by `getConfig`