Add buildkite caching to our verify pipeline.

I'm not sure why we're doing this ourselves instead of using
buildkite's own artifact caching, but that's fine.

This speeds up the "bundle install" phase from ~3m to ~20s.

Signed-off-by: Ryan Davis <zenspider@chef.io>

.expeditor/buildkite/verify.sh

@@ -1,10 +1,23 @@
 #!/bin/bash
 
-set -ueo pipefail
+set -ue
 
+echo "--- dependencies"
 export LANG=C.UTF-8 LANGUAGE=C.UTF-8
+S3_URL="s3://public-cd-buildkite-cache/${BUILDKITE_PIPELINE_SLUG}/${BUILDKITE_LABEL}"
+
+pull_s3_file() {
+    aws s3 cp "${S3_URL}/$1" "$1" || echo "Could not pull $1 from S3"
+}
+
+push_s3_file() {
+    if [ -f "$1" ]; then
+        aws s3 cp "$1" "${S3_URL}/$1" || echo "Could not push $1 to S3 for caching."
+    fi
+}
+
 apt-get update -y
-apt-get install sudo -y
+apt-get install sudo awscli -y
 
 echo "--- setting up user"
 useradd -m -U --uid 2000 normal
@@ -19,8 +32,25 @@ gem env
 bundle --version
 
 echo "--- bundle install"
+pull_s3_file "bundle.tar.gz"
+pull_s3_file "bundle.sha256"
+
+if [ -f bundle.tar.gz ]; then
+  tar -xzf bundle.tar.gz
+fi
+
+bundle config --local path vendor/bundle
 bundle install --jobs=7 --retry=3 --without tools maintenance deploy
 
+if [[ -f bundle.tar.gz && -f bundle.sha256 ]] && shasum --check bundle.sha256 --status; then
+    echo "Bundled gems have not changed. Skipping upload to s3"
+else
+    shasum -a 256 vendor/bundle > bundle.sha256
+    tar -czf bundle.tar.gz vendor/
+    push_s3_file bundle.tar.gz
+    push_s3_file bundle.sha256
+fi
+
 echo "+++ bundle exec rake"
 # TODO: run this as non-root:
 # chown -R normal:normal /home/normal /workdir