Re-add init test db script

docker/mysql/init_db_d/create_test_db.sh

+#!/usr/bin/env sh
+
+DB_NAME="${MYSQL_DATABASE}_test"
+mysql -u root -p${MYSQL_ROOT_PASSWORD} -e "CREATE DATABASE IF NOT EXISTS ${DB_NAME};"
+mysql -u root -p${MYSQL_ROOT_PASSWORD} -e "GRANT ALL ON ${DB_NAME}.* TO '$MYSQL_USER'@'%';"
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