Lightning: lightning_metadata not deleted after import exit successfully

[fubinzh]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

• Create a new tidb cluster
• Enable tidb_enable_list_partition on Tidb
• Import list partition test data (1.5k tables)
  data source: s3://nfs/tools_test_data/list_partition_1.5k?access-key=minioadmin&secret-access-key=minioadmin&endpoint=http%3a%2f%2fminio.pingcap.net%3a9000&force-path-style=true
• After lightning import, check tidb whether lightning_metadata database was deleted.

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

lightning_metadata database should be deleted.

3. What did you see instead (Required)

lightning_metadata not deleted through lightning import was successful.

Lightning log:
tidb lightning exit
2021-09-16T14:35:44.012Z INFO host/host.go:41 Execute command finished {"command": "/tidb-lightning "-tidb-port" "4000" "-tidb-user" "root" "-tidb-password" "" "-backend" "local" "-sorted-kv-dir" "/tmp/sorted-kv-dir" "-d" "s3://nfs/tools_test_data/list_partition_1.5k?access-key=minioadmin&secret-access-key=minioadmin&endpoint=http%3a%2f%2fminio.pingcap.net%3a9000&force-path-style=true" "-pd-urls" "upstream-pd.brie-acceptance-long-time-demo-9trtr.svc:2379" "-tidb-host" "upstream-tidb.brie-acceptance-
long-time-demo-9trtr.svc"", "execute duration": "37m33.076334571s"}

4. What is your TiDB version? (Required)

/ # ./tidb-lightning -V
Release Version: v5.2.0-nightly
Git Commit Hash: b839744
Git Branch: heads/refs/tags/v5.2.0-nightly
Go Version: go1.16.4
UTC Build Time: 2021-09-17 01:40:14
Race Enabled: false