Prepare MariaDB restore tests and recover backup disk space safely

usr-local-sbin/app-restore-test.sh

@@ -14,6 +14,7 @@ while (( $# )); do
     --config) CONFIG_FILE=${2:?Missing config}; shift 2 ;;
     --check) MODE=check; shift ;;
     --cleanup) MODE=cleanup; shift ;;
+    --prepare-db) MODE=prepare; shift ;;
     --remote-run) REMOTE_RUN=${2:?Missing run}; shift 2 ;;
     --help) echo 'Usage: app-restore-test.sh [--config FILE] [--check | --cleanup] [--remote-run NAME]'; exit 0 ;;
     *) die "Unknown argument: $1" ;;