etcd: ssh: Pass through the ctx into the SSH dialer

I hope I did this correctly.

etcd/ssh/ssh.go

@@ -241,7 +241,7 @@ func (obj *World) Connect(ctx context.Context, init *engine.WorldInit) error {
 	}
 
 	obj.init.Logf("ssh: %s@%s", user, addr)
-	obj.sshClient, err = ssh.Dial("tcp", addr, sshConfig)
+	obj.sshClient, err = dialSSHWithContext(ctx, "tcp", addr, sshConfig)
 	if err != nil {
 		return err
 	}
@@ -341,3 +341,20 @@ func (obj *World) cleanup() error {
 func (obj *World) Cleanup() error {
 	return obj.cleanup()
 }
+
+// dialSSHWithContext wraps ssh.Dial so that we can have a context to cancel.
+func dialSSHWithContext(ctx context.Context, network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
+	dialer := &net.Dialer{}
+	conn, err := dialer.DialContext(ctx, network, addr)
+	if err != nil {
+		return nil, err
+	}
+
+	c, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	return ssh.NewClient(c, chans, reqs), nil
+}