[7.x] Automatically retry 'docker pull' on CI

.ci/run-elasticsearch.sh

@@ -157,6 +157,16 @@ fi
 
 echo -e "\033[34;1mINFO:\033[0m Starting container $NODE_NAME \033[0m"
 
+# Pull the container, retry on failures up to 5 times with
+# short delays between each attempt. Fixes most transient network errors.
+docker_pull_attempts=0
+until [ "$docker_pull_attempts" -ge 5 ]
+do
+   docker pull docker.elastic.co/elasticsearch/"$ELASTICSEARCH_VERSION" && break
+   docker_pull_attempts=$((docker_pull_attempts+1))
+   sleep 10
+done
+
 set -x
 docker run \
   --name "$NODE_NAME" \