- Add 'docker compose down -v' before starting services to clean up stale volumes
- Prevents accumulation of data/buckets from previous test runs
- Add volume registration verification after service startup
- Check that volume server has registered with master and volumes are available
- Helps diagnose 'No writable volumes' errors
- Shows volume count and waits up to 30 seconds for volumes to be created
- Both spark-tests and spark-example jobs updated with same improvements