CI: fixed exit code of test environment startup script

Author: rashtao

docker/startup.sh

@@ -8,10 +8,15 @@ KC=${KC:=false}
 set -e
 
 ./docker/start_db.sh &
+START_DB_PID=$!
+
 ./docker/start_kafka_zk.sh
+./docker/start_schema_registry.sh &
+START_SCHEMA_REGISTRY_PID=$!
+
 if [ "$KC" == "true" ]; then
-  ./docker/start_kafka_connect.sh &
+  ./docker/start_kafka_connect.sh
 fi
-./docker/start_schema_registry.sh &
 
-wait
+wait $START_DB_PID
+wait $START_SCHEMA_REGISTRY_PID