pkg: Add LCOW init package

This package build the init filesystem for LCOW (Linux Containers
on Windows) based on the instructions from:
https://github.com/Microsoft/opengcs.git

We also pull in a udhcpd config script from a specific version of
busybox which was the tip of master at the time this was added.

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

pkg/init-lcow/Dockerfile

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+FROM linuxkit/alpine:3744607156e6b67e3e7d083b15be9e7722215e73 AS mirror
+RUN mkdir -p /out/etc/apk && cp -r /etc/apk/* /out/etc/apk/
+RUN apk add --no-cache --initdb -p /out \
+    alpine-baselayout \
+    busybox \
+    e2fsprogs \
+    musl
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
+
+FROM linuxkit/alpine:3744607156e6b67e3e7d083b15be9e7722215e73 AS build
+RUN apk add --no-cache build-base curl git go musl-dev
+ENV GOPATH=/go PATH=$PATH:/go/bin
+ENV OPENGCS_COMMIT=4e4e6f28a03e974e6c32f00a91d51f9605821fdd
+RUN git clone https://github.com/Microsoft/opengcs.git /go/src/github.com/Microsoft/opengcs && \
+    cd /go/src/github.com/Microsoft/opengcs && \
+    git checkout $OPENGCS_COMMIT && \
+    cd service && \
+    make
+RUN mkdir /out && \
+    cp -r /go/src/github.com/Microsoft/opengcs/service/bin /out/bin && \
+    cp /go/src/github.com/Microsoft/opengcs/kernelconfig/4.11/scripts/init_script /out/init && \
+    chmod ugo+rx /out/init && \
+    mkdir /out/sbin && \
+    curl -fSL "https://raw.githubusercontent.com/mirror/busybox/38d966943f5288bb1f2e7219f50a92753c730b14/examples/udhcp/simple.script" -o /out/sbin/udhcpc_config.script && \
+    chmod ugo+rx /out/sbin/udhcpc_config.script && \
+    mkdir -p /out/root/integration && \
+    cp /go/src/github.com/Microsoft/opengcs/kernelconfig/4.11/prebuildSandbox.vhdx /out/root/integration/prebuildSandbox.vhdx
+
+# This d line below should be removed once
+# https://github.com/Microsoft/opengcs/issues/52 is addressed and then
+# runc should be added via the YAML file
+FROM linuxkit/runc:a0f2894e50bacbd1ff82be41edff8b8e06e0b161 AS runc
+
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=mirror /out/ /
+COPY --from=build /out/ /
+COPY --from=runc /usr/bin/runc /sbin/runc
+

pkg/init-lcow/Makefile

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+IMAGE=init-lcow
+NETWORK=1
+
+include ../package.mk