vendor: add buildkit

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

vendor/github.com/moby/buildkit/client/client_unix.go

@@ -0,0 +1,19 @@
+// +build !windows
+
+package client
+
+import (
+	"net"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+func dialer(address string, timeout time.Duration) (net.Conn, error) {
+	addrParts := strings.SplitN(address, "://", 2)
+	if len(addrParts) != 2 {
+		return nil, errors.Errorf("invalid address %s", address)
+	}
+	return net.DialTimeout(addrParts[0], addrParts[1], timeout)
+}