Some tables may not be physically dropped on TiFlash

[JaySon-Huang]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Apply the following three DDLs quickly
2. Create a table on tidb
3. Add tiflash for the table
4. drop the table

There is a chance that the drop table is executed on TiFlash before the IStorage instance is actually created by applying snapshot.
Then the information that the table has been dropped is missed on the TiFlash instance and its related data can not be physically dropped.

This can be workaround by restarting TiFlash, which will re-sync all table info from TiDB. And it will mark the table as tombstones at that time.

logging from testing pipeline : table_id_571.log

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

3. What did you see instead (Required)

4. What is your TiFlash version? (Required)

https://github.com/pingcap/tiflash/tree/5ba01c04abc057f376eb71c8598cab65bc711460