Essential parameter in the hook needs to be handled

[asn1809]

When executing hooks, check for the parameter essential and follow the below guidelines for implementing the same:

Defines whether the hook is essential for a successful backup. Hooks defined as essential (which is the default) need to be processed successfully, otherwise the overall backup operation is considered to be fatally failed. In this case a rollback is initiated and the workflow is not process any further. For non-essential hooks an unsuccessful execution is tolerated, the processing of the workflow continues and the backup is reported as successful. The flag is only considered if the workflow is configured with "fail-on=essential-error". See workflow section for details.