fix the test for embedded

mysql-test/suite/innodb/t/innodb-truncate.test

 --source include/have_innodb.inc
+let $datadir=`select @@datadir`;
 --echo #
 --echo # TRUNCATE TABLE
 --echo #
@@ -72,6 +73,7 @@ SET FOREIGN_KEY_CHECKS= ON;
 CREATE TABLE t2 (f2 INT, FOREIGN KEY(f2) REFERENCES t1 (f2)) ENGINE=InnoDB;
 --error ER_CANT_CREATE_TABLE
 CREATE TABLE t3 (a INT) ENGINE=InnoDB;
+--replace_result $datadir ./
 --error ER_ERROR_ON_RENAME
 ALTER TABLE t1 RENAME TO t3;
 ALTER TABLE t1 FORCE;