dict_create_add_foreigns_to_dictionary(): Do not commit the transaction.
The operation can still fail in dict_load_foreigns(), and we want
to be able to roll back the transaction.

create_table_info_t::create_table(): Never reset m_drop_before_rollback,
and never commit the transaction. We use a single point of rollback
in ha_innobase::create(). Merge the logic from
row_table_add_foreign_constraints().