Move alpine docker image to specific sub-dir

.buildkite/steps/build-docker-images.sh

@@ -1,6 +1,28 @@
 #!/bin/bash
 set -e
 
+build_alpine_docker_image() {
+  local image_tag="$1"
+
+  echo "--- Building :docker: $image_tag"
+  cp pkg/buildkite-agent-linux-amd64 packaging/docker/linux/buildkite-agent
+  chmod +x packaging/docker/linux/buildkite-agent
+  docker build --tag "$image_tag" packaging/docker/linux
+}
+
+test_docker_image() {
+  local image_tag="$1"
+
+  echo "--- :hammer: Testing $image_tag can run"
+  docker run --rm --entrypoint "buildkite-agent" "$image_tag" --version
+
+  echo "--- :hammer: Testing $image_tag can access docker socket"
+  docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --entrypoint "docker" "$image_tag" version
+
+  echo "--- :hammer: Testing $image_tag has docker-compose"
+  docker run --rm --entrypoint "docker-compose" "$image_tag" --version
+}
+
 echo '--- Getting agent version from build meta data'
 
 image_tag=$(buildkite-agent meta-data get "agent-docker-image-alpine")
@@ -13,19 +35,9 @@ mkdir -p pkg
 echo '--- Downloading :linux: binaries'
 buildkite-agent artifact download "pkg/buildkite-agent-linux-amd64" .
 
-echo '--- Building :docker: image'
-cp pkg/buildkite-agent-linux-amd64 packaging/docker/linux/buildkite-agent
-chmod +x packaging/docker/linux/buildkite-agent
-docker build --tag "$image_tag" packaging/docker/linux
-
-echo "--- :hammer: Testing $image_tag can run"
-docker run --rm --entrypoint "buildkite-agent" "$image_tag" --version
-
-echo "--- :hammer: Testing $image_tag can access docker socket"
-docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --entrypoint "docker" "$image_tag" version
+build_alpine_docker_image "$image_tag"
 
-echo "--- :hammer: Testing $image_tag has docker-compose"
-docker run --rm --entrypoint "docker-compose" "$image_tag" --version
+test_docker_image "$image_tag"
 
 echo '--- Pushing :docker: image to buildkiteci/agent'
 docker push "$image_tag"