cinder backup force-delete when backup is error

Update testcases to force delete a backup when the state is error

steps:
- create a backup
- reset backup state to error
- force delete the backup

Fixed create backup cleanup

Added API:
- force_delete_backup

Change-Id: I2495e9c10e888f5a01d2a3e7f09a4b6dfc3d58a0
4 files changed