Mistral sample workflow fails to create incremental backup for volume without previous backup.

[Vitalii Yerys]

Steps to reproduce:
  1. Create a volume.
  2. Add sample workflow to mistral
  3. Using Mistral try to backup volume with incremental: true (NOTE: There should be no previous backups of this specific volume). Command to use: openstack workflow execution create sample_backup_workbook.create_backups_workflow '{"volumes_id_list": ["b4f97be0-5412-4dcf-8e06-dc5cebca6ce4"], "incremental": true }'

Actual result:

Workflow is shown as running (and it stucks like that), and task list command is reproducing incorrect output:

{code}
root@node-6:~# openstack task execution list
'with_items_context'
{code}

[Taras Kostyuk (tkostyuk)]

There are actually several issues described:

The first:

The sample backup workflow when executed to create an incremental backup of a volume with no full backup fails. This is expected behavior because it's not possible to create an incremental backup of a volume with no full backup fails. Using cinder CLI also lead to an error:

# cinder backup-create --incremental b2210cf4-720b-42e6-8dc2-7930a31a87d7
ERROR: Invalid backup: No backups available to do an incremental backup. (HTTP 400) (Request-ID: req-32cc972d-cc71-46f4-aca7-8e70584ee240)

The second:

This is the failure of 'openstack task execution list' CLI command.
This is not expected but looks like Mistral(https://launchpad.net/mistral) bug.

P.S.

To get 'openstack task execution list' CLI command working delete the problematic execution.

# openstack workflow execution list
# openstack workflow execution delete <EXECUTION_ID>

[Taras Kostyuk (tkostyuk)]

Correction of User Guide made in https://review.openstack.org/#/c/368026/5..6/doc/user_guide/mistral.rst