Add options for SSH identity file and passphrase to ConnectionHelper

[znck]

Description

ConnectionHelper is used in docker terraform provider and there is a requirement to add SSH identity file or passphrase to connect in a CI/CD environment. Related terraform issue—hashicorp/terraform-provider-docker#268

[znck]

cli/cli/connhelper/connhelper.go

Lines 24 to 45 in 590f327

	func GetConnectionHelper(daemonURL string) (*ConnectionHelper, error) {
	u, err := url.Parse(daemonURL)
	if err != nil {
	return nil, err
	}
	switch scheme := u.Scheme; scheme {
	case "ssh":
	sp, err := ssh.ParseURL(daemonURL)
	if err != nil {
	return nil, errors.Wrap(err, "ssh host connection is not valid")
	}
	return &ConnectionHelper{
	Dialer: func(ctx context.Context, network, addr string) (net.Conn, error) {
	return commandconn.New(ctx, "ssh", append(sp.Args(), []string{"--", "docker", "system", "dial-stdio"}...)...)
	},
	Host: "http://docker",
	}, nil
	}
	// Future version may support plugins via ~/.docker/config.json. e.g. "dind"
	// See docker/cli#889 for the previous discussion.
	return nil, err
	}

The solution can be as simple as allowing custom arguments for ssh in GetConnectionHelper.