The ``volume backup list`` command does not show the
created_at column for backups which doesn't really
help the end-user since a critical part of a backup
is knowing when it was taken, and fast if there is
a rush doing recovery by restoring a volume from a
backup.
Change-Id: I8d8a7f36c468c9faa2c2c47bfa9ba9e1ca5b9858