desc: Tests meta operations in composite queries
tests:

    - py: r.expr([1,2,3]).for_each(r.db_create('db_' + r.row.coerce_to('string')))
      ot: ({'dbs_created':3,'config_changes':arrlen(3)})

    - py: |
        r.db_list().set_difference(["rethinkdb", "test"]).for_each(lambda db_name:
            r.expr([1,2,3]).for_each(lambda i:
                r.db(db_name).table_create('tbl_' + i.coerce_to('string'))))
      ot: partial({'tables_created':9})

    - py: r.db_list().set_difference(["rethinkdb", "test"]).for_each(r.db_drop(r.row))
      ot: partial({'dbs_dropped':3,'tables_dropped':9})