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/.travis.yml

@@ -0,0 +1,24 @@
+language: go
+
+go:
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
+
+go_import_path: google.golang.org/appengine
+
+install:
+  - go get -u -v $(go list -f '{{join .Imports "\n"}}{{"\n"}}{{join .TestImports "\n"}}' ./... | sort | uniq | grep -v appengine)
+  - mkdir /tmp/sdk
+  - curl -o /tmp/sdk.zip "https://storage.googleapis.com/appengine-sdks/featured/go_appengine_sdk_linux_amd64-1.9.40.zip"
+  - unzip -q /tmp/sdk.zip -d /tmp/sdk
+  - export PATH="$PATH:/tmp/sdk/go_appengine"
+  - export APPENGINE_DEV_APPSERVER=/tmp/sdk/go_appengine/dev_appserver.py
+
+script:
+  - goapp version
+  - go version
+  - go test -v google.golang.org/appengine/...
+  - go test -v -race google.golang.org/appengine/...
+  - goapp test -v google.golang.org/appengine/...