tools: Use the Alpine base to build the go-compile image

Also, convert to use a git tree hash.

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

tools/go-compile/Dockerfile

@@ -1,10 +1,16 @@
-FROM alpine:3.5
-RUN apk update && apk add --no-cache build-base git go
+FROM linuxkit/alpine:451603daf499e3a40308dbf5571dcffed2343ffa 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 \
+    git \
+    go \
+    musl-dev
+RUN rm -rf /out/etc/apk /out/lib/apk /out/var/cache
+
+FROM scratch
 ENV GOPATH=/go PATH=$PATH:/go/bin
-RUN go get -u github.com/golang/lint/golint && \
-    go get -u github.com/gordonklaus/ineffassign && \
-    go get -u github.com/LK4D4/vndr
-
-COPY . ./
-
+COPY --from=mirror /out/ /
+COPY --from=mirror /go/bin/ /go/bin/
+COPY /compile.sh /compile.sh
 ENTRYPOINT ["/compile.sh"]