new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/google.golang.org/appengine/internal/app_id.go

@@ -0,0 +1,28 @@
+// Copyright 2011 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package internal
+
+import (
+	"strings"
+)
+
+func parseFullAppID(appid string) (partition, domain, displayID string) {
+	if i := strings.Index(appid, "~"); i != -1 {
+		partition, appid = appid[:i], appid[i+1:]
+	}
+	if i := strings.Index(appid, ":"); i != -1 {
+		domain, appid = appid[:i], appid[i+1:]
+	}
+	return partition, domain, appid
+}
+
+// appID returns "appid" or "domain.com:appid".
+func appID(fullAppID string) string {
+	_, dom, dis := parseFullAppID(fullAppID)
+	if dom != "" {
+		return dom + ":" + dis
+	}
+	return dis
+}