vendor: update buildkit to v0.8

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/util/sshutil/keyscan.go

@@ -0,0 +1,51 @@
+package sshutil
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+
+	"golang.org/x/crypto/ssh"
+)
+
+const defaultPort = 22
+
+var errCallbackDone = fmt.Errorf("callback failed on purpose")
+
+// addDefaultPort appends a default port if hostport doesn't contain one
+func addDefaultPort(hostport string, defaultPort int) string {
+	_, _, err := net.SplitHostPort(hostport)
+	if err == nil {
+		return hostport
+	}
+	hostport = net.JoinHostPort(hostport, strconv.Itoa(defaultPort))
+	return hostport
+}
+
+// SshKeyScan scans a ssh server for the hostkey; server should be in the form hostname, or hostname:port
+func SSHKeyScan(server string) (string, error) {
+	var key string
+	KeyScanCallback := func(hostport string, remote net.Addr, pubKey ssh.PublicKey) error {
+		hostname, _, err := net.SplitHostPort(hostport)
+		if err != nil {
+			return err
+		}
+		key = strings.TrimSpace(fmt.Sprintf("%s %s", hostname, string(ssh.MarshalAuthorizedKey(pubKey))))
+		return errCallbackDone
+	}
+	config := &ssh.ClientConfig{
+		HostKeyCallback: KeyScanCallback,
+	}
+
+	server = addDefaultPort(server, defaultPort)
+	conn, err := ssh.Dial("tcp", server, config)
+	if key != "" {
+		// as long as we get the key, the function worked
+		err = nil
+	}
+	if conn != nil {
+		conn.Close()
+	}
+	return key, err
+}