br need to retry scatter if reply status is not SUCCESS

[Leavrth]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

br sends scatter request, and pd returns CANCEL response.

2. What did you expect to see? (Required)

br retries to send the request

3. What did you see instead (Required)

br ignores it.

4. What is your TiDB version? (Required)

master

[Leavrth]

/component br

[Leavrth]

/severity major

[Leavrth]

/affects-7.1

[Leavrth]

/label affects-6.5
/label affects-7.1
/remove-label may-affects-*