pkg: Roll the swap package from linuxkit/alpine

Also convert to a multi-stage build and make the
make the HUB org/registry build time configurable.

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

pkg/swap/Dockerfile

@@ -1,13 +1,17 @@
-FROM alpine:3.5
+FROM linuxkit/alpine:6336329f15b4166514782eaa555cf0ffd35c519c@sha256:f6c2ce92910b1d6e4e5557850a554f4a3ae9f66c1e89ad86a24d6c6e550f165e 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 \
+    cryptsetup \
+    musl \
+    util-linux
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
 
-# swap command - only minimal Alpine install
-
-# use util-linux to get swapfile utils, cryptsetup
-#   at some point, hopefully use our own mkswap and swapon, as well as cryptsetup
-RUN apk add --update util-linux cryptsetup
-
-# add the entrypoint and make it executable
-COPY . ./
-
-# ENTRYPOINT
-ENTRYPOINT swap.sh
+FROM scratch
+ENTRYPOINT []
+CMD []
+WORKDIR /
+COPY --from=mirror /out/ /
+COPY /swap.sh .
+ENTRYPOINT ["swap.sh"]