imitate ssh.Dial func for simplicity

previously ScanHostKey ignored any SSH/network errors
in case it managed to get host keys

to make it more obvious we imitate `ssh.Dial` with `sshDial` func

Signed-off-by: Artem Nistratov <nistratov.artem@gmail.com>

Author: adone

ssh/host_key.go

@@ -47,24 +47,31 @@ func ScanHostKey(host string, timeout time.Duration, clientHostKeyAlgos []string
 		config.HostKeyAlgorithms = clientHostKeyAlgos
 	}
 
-	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	err := sshDial(host, config)
+
+	if len(col.knownKeys) > 0 {
+		return col.knownKeys, nil
+	}
+
+	return col.knownKeys, err
+}
+
+func sshDial(host string, config *ssh.ClientConfig) error {
+	ctx, cancel := context.WithTimeout(context.Background(), config.Timeout)
 	defer cancel()
-	// support for ALL_PROXY ENV varaible
+	// this reads the ALL_PROXY environment varaible
 	conn, err := proxy.Dial(ctx, "tcp", host)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	c, chans, reqs, err := ssh.NewClientConn(conn, host, config)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	client := ssh.NewClient(c, chans, reqs)
 	defer client.Close()
 
-	if len(col.knownKeys) > 0 {
-		return col.knownKeys, nil
-	}
-	return col.knownKeys, err
+	return nil
 }
 
 // HostKeyCollector offers a StoreKey method which provides an