Re-enable a test that was disabled as collateral damage.

Starting with MySQL 5.5, queries will acquire and hold a shared meta-data lock
(MDL) on tables they process, until the transaction is committed or
rolled back. This will prevent DDL operations on the tables, such as creating
an index.

innodb-index.test: Use a second table for creating the index. The index will
still be "too new" for the transaction that was started before the index
creation was started.