Do fast exit with error code and FATAL ERROR message, if innodb cannot start during prepare.

Otherwise, it is possible for "prepare" to exit with error code 0,
even if it did not work at all.

extra/mariabackup/xtrabackup.cc

@@ -1989,10 +1989,8 @@ static bool innodb_init()
 {
 	dberr_t err = innobase_start_or_create_for_mysql();
 	if (err != DB_SUCCESS) {
-		msg("mariabackup: innodb_init() returned %d (%s).",
+		die("mariabackup: innodb_init() returned %d (%s).",
 		    err, ut_strerr(err));
-		innodb_shutdown();
-		return(TRUE);
 	}
 
 	return(FALSE);