[CI] Stop gradle processes between tasks in packer cache

Author: brianseeders

.buildkite/packer_cache.sh

@@ -30,5 +30,7 @@ for branch in "${branches[@]}"; do
 
   export JAVA_HOME="$HOME/.java/$ES_BUILD_JAVA"
   "checkout/${branch}/gradlew" --project-dir "$CHECKOUT_DIR" --parallel -s resolveAllDependencies -Dorg.gradle.warning.mode=none -DisCI --max-workers=4
+  "checkout/${branch}/gradlew" --stop
+  pkill -f '.*GradleDaemon.*'
   rm -rf "checkout/${branch}"
 done