[TD-3192] <feature>: support supertable limit and offset.

src/kit/taosdemo/insert.json

@@ -38,7 +38,9 @@
 			"auto_create_table": "no",
 			"data_source": "rand",
 			"insert_mode": "taosc",
-			"insert_rows": 100000,
+            "childtable_limit": 33,
+            "childtable_offset": 33,
+			"insert_rows": 1000,
 			"multi_thread_write_one_tbl": "no",
 			"number_of_tbl_in_one_sql": 0,
 			"rows_per_tbl": 100,