Offline-snapshot unlock dynamodb if error

[mbloch1986]

To check if a offline-snapshot is already in process the lambda function aem_offline_snapshot.py set a lock state to the dynamo db e.g.
command_id | String | : | michaelb-aem63_backup_lock

This lock dosn't get cleared after the lambda function raise an error, even before a offline-snapshot could be taken.