When trying to list backups of a deleted volume with --volume,
openstackclient fails because the volume does not exist.
However, for listing a volume's backups, the volume itself
does not need to be present.
Fix this issue by allowing the volume of the requested backups
to not exist.
Story: 2009901
Task: 44716
Change-Id: Iea1a567151f427fa0e1ccff3af5cbeab620defcd
Signed-off-by: Jan Hartkopf <jhartkopf@inovex.de>
8acead32ee