Update docker-setup.sh to not preemptively pull snapshot images anymore (#67)

the docker compose will pull the images during build, so it's no necessary to pull the snapshot images upfront.

it should still check if they exist though, so we can gracefully handle the case when previous/current/next are missing.

Author: jsvd

docker-setup.sh

@@ -4,13 +4,13 @@
 # Ensure you have Docker installed locally and set the ELASTIC_STACK_VERSION environment variable.
 set -e
 
-pull_docker_snapshot() {
+check_docker_snapshot() {
   project="${1?project name required}"
   stack_version_alias="${2?stack version alias required}"
   local docker_image="docker.elastic.co/${project}/${project}${DISTRIBUTION_SUFFIX}:${ELASTIC_STACK_VERSION}"
-  echo "Pulling $docker_image"
-  if docker pull "$docker_image" ; then
-    echo "docker pull successful"
+  echo "Checking manifest for $docker_image"
+  if docker manifest inspect "$docker_image" ; then
+    echo "docker image exists. proceeding..."
   else
     case $stack_version_alias in
       "8.previous"|"8.current"|"8.next"|"8.future")
@@ -65,7 +65,7 @@ export DISTRIBUTION_SUFFIX
 echo "Testing against version: $ELASTIC_STACK_VERSION (distribution: ${DISTRIBUTION:-"default"})"
 
 if [[ "$ELASTIC_STACK_VERSION" = *"-SNAPSHOT" ]]; then
-    pull_docker_snapshot "logstash" $ELASTIC_STACK_VERSION_ALIAS
+    check_docker_snapshot "logstash" $ELASTIC_STACK_VERSION_ALIAS
 fi
 
 if [ -f Gemfile.lock ]; then