update Dockerfile to multi-stage

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

Dockerfile

-FROM golang:1.10-alpine
+FROM golang:1.11-alpine AS build
 ENV DISTRIBUTION_DIR /go/src/github.com/docker/distribution
 ENV DOCKER_BUILDTAGS include_oss include_gcs
@@ -7,14 +7,15 @@ ARG GOOS=linux
 ARG GOARCH=amd64
 RUN set -ex \
-    && apk add --no-cache make git
+    && apk add --no-cache make git file
 WORKDIR $DISTRIBUTION_DIR
 COPY . $DISTRIBUTION_DIR
-COPY cmd/registry/config-dev.yml /etc/docker/registry/config.yml
-
-RUN make PREFIX=/go clean binaries
+RUN CGO_ENABLED=0 make PREFIX=/go clean binaries && file ./bin/registry | grep "statically linked"
+FROM alpine
+COPY cmd/registry/config-dev.yml /etc/docker/registry/config.yml
+COPY --from=build /go/src/github.com/docker/distribution/bin/registry /bin/registry
 VOLUME ["/var/lib/registry"]
 EXPOSE 5000
 ENTRYPOINT ["registry"]