func (s *Sentinel) close() {
	if s.pools != nil {
		for _, pool := range s.pools {
			pool.Close()
		}
	}
	s.pools = nil
}
func (s *Sentinel) close() {
	if s.pools != nil {
		for _, pool := range s.pools {
			pool.Close()
		}
	}
	s.pools = nil
}
// close connection pool to Sentinel.
// Lock must be hold by caller.