[#171] pool: Close only dialed connections

To avoid panics during close operation, close
only dialed connections.

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

pool/pool.go

@@ -86,6 +86,8 @@ type client interface {
 type clientStatus interface {
 	// isHealthy checks if the connection can handle requests.
 	isHealthy() bool
+	// isDialed checks if the connection was created.
+	isDialed() bool
 	// setUnhealthy marks client as unhealthy.
 	setUnhealthy()
 	// address return address of endpoint.
@@ -2809,10 +2811,12 @@ func (p *Pool) Close() {
 	// close all clients
 	for _, pools := range p.innerPools {
 		for _, cli := range pools.clients {
+			if cli.isDialed() {
 				_ = cli.close()
 			}
 		}
 	}
+}
 
 // SyncContainerWithNetwork applies network configuration received via
 // the Pool to the container. Changes the container if it does not satisfy