meta: checkpoint using source-id as the identifier but online DDL using server-id

[csuzhangxc]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.

replace a DM-worker instance with another DM-worker instance with the same source-id, but report ghost table not found when replicating online DDL operation.

2. What did you expect to see?

task keeps running.

3. What did you see instead?

task is paused

4. Versions of the cluster

   • DM version (run dmctl -V or dm-worker -V or dm-master -V):

     any version before commit `1173d269309c79f45b8d0897247e22f0a714c39d`
     

[csuzhangxc]

fixed in #494.