operator get blocked when delete backup CR

[lichunzhu]

Bug Report

What version of Kubernetes are you using?

v1.12.2

What version of TiDB Operator are you using?

v1.1.0-beta.1.471+ae25bc38e10f3c-dirty

What did you do?

delete backup CR whose backuped files on S3 has been delete manually by myself.

What did you expect to see?
delete backup CR successfully.

What did you see instead?
It gets blocked. error log:

Create rclone.conf file.
/tidb-backup-manager clean --namespace=demo --backupName=basic-backup
I0710 03:41:08.633373       1 clean.go:69] start to clean backup demo/basic-backup
E0710 03:41:09.430348       1 manager.go:79] clean cluster demo/basic-backup backup s3://chunzhu/backup-2020-07-09T06:31:00Z.tgz failed, err: cluster demo/basic-backup, execute rclone deletefile command failed, output: 2020/07/10 03:41:09 ERROR : Attempt 1/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 ERROR : Attempt 2/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 ERROR : Attempt 3/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 Failed to deletefile: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
, err: exit status 1
I0710 03:41:09.440879       1 backup_status_updater.go:66] Backup: [demo/basic-backup] updated successfully
error: cluster demo/basic-backup, execute rclone deletefile command failed, output: 2020/07/10 03:41:09 ERROR : Attempt 1/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 ERROR : Attempt 2/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 ERROR : Attempt 3/3 failed with 1 errors and: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
2020/07/10 03:41:09 Failed to deletefile: s3:chunzhu/backup-2020-07-09T06:31:00Z.tgz is a directory or doesn't exist
, err: exit status 1