rollback distributed adding index is not handled correctly.

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set global tidb_enable_dist_task=1;
creating an index on a large table and cancel it.

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

The next add index SQL will use ingest way to add index again.

3. What did you see instead (Required)

The next add index SQL won't use ingest way to add index.

4. What is your TiDB version? (Required)

master