Add script to extract binaries from prebuilt cli-bin image (#1388)

Signed-off-by: Kevin Lingerfelt <kl@buoyant.io>

bin/docker-pull-binaries

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+set -eu
+
+if [ $# -eq 1 ]; then
+    tag="${1:-}"
+else
+    echo "usage: $(basename $0) tag" >&2
+    exit 64
+fi
+
+bindir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+rootdir="$( cd $bindir/.. && pwd )"
+
+. $bindir/_docker.sh
+
+workdir="$rootdir/target/release"
+mkdir -p "$workdir"
+
+shorttag="$tag"
+if [ "${tag:0:1}" == "v" ]; then
+  shorttag="${tag:1}"
+fi
+
+# create the cli-bin container in order to extract the binaries
+id=$(docker create "$(docker_repo cli-bin):$tag")
+
+for os in darwin linux windows ; do
+  ext="$os"
+  if [ "$os" == "windows" ]; then
+    ext="windows.exe"
+  fi
+  filepath="$workdir/linkerd2-cli-$shorttag-$ext"
+  docker cp "$id:/out/linkerd-$os" "$filepath"
+  openssl dgst -sha256 "$filepath" | awk '{print $2}' > "$filepath.sha256"
+  echo "$filepath"
+done
+
+# cleanup the cli-bin container when finished
+docker rm "$id" > /dev/null