hack: base build scripts

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

hack/dockerfiles/vendor.Dockerfile

@@ -0,0 +1,18 @@
+# syntax = docker/dockerfile:1.0-experimental
+FROM golang:1.12-alpine AS vendored
+RUN  apk add --no-cache git
+WORKDIR /src
+RUN --mount=target=/src,rw \
+  --mount=target=/go/pkg/mod,type=cache \
+  go mod tidy && go mod vendor && \
+  mkdir /out && cp -r go.mod go.sum vendor /out
+
+FROM scratch AS update
+COPY --from=vendored /out /out
+
+FROM vendored AS validate
+RUN --mount=target=.,rw \
+  git add -A && \
+  rm -rf vendor && \
+  cp -rf /out/* . && \
+  ./hack/validate-vendor check