Exchange operator should check the schema before sending/receiver data

[windtalker]

Exchange operator is used to shuffle data in mpp, the schema of a exchange operator is generated in compile time based on DAG request, there is a chance that TiDB has some bugs so the data type is DAG request is not the same as the actually data type in runtime, which mean Exchange operator may send/receiver data that is not the same as its schema. We should check the schema and throw error if this happens.

[tisonkun]

related to #1492