vendor: update moby/buildkit

Update modules:

  go mod edit -require github.com/moby/buildkit@master
  go mod tidy -compat=1.17 && ./hack/update-vendor

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/github.com/moby/buildkit/client/connhelper/dockercontainer/dockercontainer.go

@@ -0,0 +1,56 @@
+// Package dockercontainer provides connhelper for docker-container://<container>
+package dockercontainer
+
+import (
+	"context"
+	"net"
+	"net/url"
+
+	"github.com/docker/cli/cli/connhelper/commandconn"
+	"github.com/moby/buildkit/client/connhelper"
+	"github.com/pkg/errors"
+)
+
+func init() {
+	connhelper.Register("docker-container", Helper)
+}
+
+// Helper returns helper for connecting to a Docker container.
+// Requires BuildKit v0.5.0 or later in the container.
+func Helper(u *url.URL) (*connhelper.ConnectionHelper, error) {
+	sp, err := SpecFromURL(u)
+	if err != nil {
+		return nil, err
+	}
+	return &connhelper.ConnectionHelper{
+		ContextDialer: func(ctx context.Context, addr string) (net.Conn, error) {
+			ctxFlags := []string{}
+			if sp.Context != "" {
+				ctxFlags = append(ctxFlags, "--context="+sp.Context)
+			}
+			// using background context because context remains active for the duration of the process, after dial has completed
+			return commandconn.New(context.Background(), "docker", append(ctxFlags, []string{"exec", "-i", sp.Container, "buildctl", "dial-stdio"}...)...)
+		},
+	}, nil
+}
+
+// Spec
+type Spec struct {
+	Context   string
+	Container string
+}
+
+// SpecFromURL creates Spec from URL.
+// URL is like docker-container://<container>?context=<context>
+// Only <container> part is mandatory.
+func SpecFromURL(u *url.URL) (*Spec, error) {
+	q := u.Query()
+	sp := Spec{
+		Context:   q.Get("context"),
+		Container: u.Hostname(),
+	}
+	if sp.Container == "" {
+		return nil, errors.New("url lacks container name")
+	}
+	return &sp, nil
+}