sql: Include primary key in secondary indices

Closes #2187

sql: Call Tarantool in OP_Clear explicitly

     * Restore sqlite3BtreeClearTable function since it's also used to
       truncate ephemeral tables which are backed by SQLite BTree-s.
       Ephemeral tables are needed to implement some SORT-s and JOIN-s.
     * OP_Clear truncates regular tables, backed by Tarantool storage
       layer. Invoke Tarantool truncate method explicitly from opcode
       handler.
     * Add regression test.