tools: Move tini to ./tools and convert to multi-stage build

Previously the "tini" contained the entire build. Using the
multi-stage build creates a new "tini" base image, which only
contains the "/bin/tini". This image can be used as the base
image for packages requiring "tini".

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

tools/tini/Dockerfile

@@ -0,0 +1,13 @@
+FROM linuxkit/c-compile:f52f485825c890d581e82a62af6906c1d33d8e5d@sha256:473fd283a090d3546e93915adacf00c69a23ff615c95c968c4a40e8723985853 AS tini-build
+COPY . /
+ENV TINI_VERSION=0.13.0
+ADD https://github.com/krallin/tini/archive/v${TINI_VERSION}.tar.gz tini-${TINI_VERSION}.tar.gz
+
+RUN zcat tini-${TINI_VERSION}.tar.gz | tar xvf -
+RUN cd tini-${TINI_VERSION} && cmake . && make && cp -a tini-static /bin/tini
+
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=tini-build bin/tini bin/tini

tools/tini/Makefile

@@ -0,0 +1,26 @@
+.PHONY: tag push
+default: push
+
+IMAGE=tini
+SHA_IMAGE=alpine:3.5@sha256:dfbd4a3a8ebca874ebd2474f044a0b33600d4523d03b0df76e5c5986cb02d7e8
+DEPS=Dockerfile Makefile
+
+hash: $(DEPS)
+	find $^ -type f | xargs cat | docker run --rm -i $(SHA_IMAGE) sha1sum - | sed 's/ .*//' > hash
+
+tag: hash
+	docker pull linuxkit/$(IMAGE):$(shell cat hash) || \
+		(docker build --no-cache -t $(IMAGE):build . && \
+		 docker tag $(IMAGE):build linuxkit/$(IMAGE):$(shell cat hash))
+
+push: tag
+	docker pull linuxkit/$(IMAGE):$(shell cat hash) || \
+		docker push linuxkit/$(IMAGE):$(shell cat hash)
+	rm -f hash
+	docker rmi $(IMAGE):build || true
+
+clean:
+	rm -f hash
+	docker rmi $(IMAGE):build || true
+
+.DELETE_ON_ERROR:

tools/tini/README.md

@@ -0,0 +1,4 @@
+[tini](https://github.com/krallin/tini) is a tiny program which can be
+used as a minimal `init` process for container images.
+
+The `linuxkit/tini` image just contains `/bin/tini` and can be used as the base image by packages, requiring `tini`.