Fix bugs in migration script

[wwwjn]

Reasons for making this change

After testing on dev environment, we find more bugs in migration script.

Related issues

Screenshots

Checklist

• I've added a screenshot of the changes, if this is a frontend change
• I've added and/or updated tests, if this is a backend change
• I've run the pre-commit.sh script
• I've updated docs, if needed

[wwwjn]

There is still another thing that needs to be fixed:

If a user first uploads a bundle to Azure Blob storage and changes the database pointing to Azure Blob storage, then the user re-runs the script to delete the original bundle storage, the script can not find the original bundle location. Since we migrate step by step, we need to store state information somewhere.

Possible solution:
When changing the database, write (original_bundle_location, target_bundle_location) to the log file. If the user wants to delete the original bundle, read through the log file and remove the original bundle files.

Working on this.