ndb - make sure all used tables are dropped in beginning of test case

mysql-test/t/ndb_index_unique.test:
  Drop table t8 in beginning of test as it's used

mysql-test/t/ndb_index_unique.test

 -- source include/have_ndb.inc
 
 --disable_warnings
-drop table if exists t1, t2, t3, t4, t5, t6, t7;
+drop table if exists t1, t2, t3, t4, t5, t6, t7, t8;
 --enable_warnings
 
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