Prevent KeyError getting value of optional data

[Nguyen Luu Hoang Minh]

Problem: Some of optional data is retrieved in this way:
        backup_name = data['backup_name'] or None
        volume_id = data['volume_id'] or None

etc...

When the key does not exist, KeyError will be raised.
Moreover, or None here is meaningless.

Solution:
Change to
        backup_name = data.get('backup_name')
        volume_id = data.get('volume_id')

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/horizon/+/919430