ZFS-backed block devices may contain just the bare device name and
not have extra options like `,size=foo`, `,format=qcow2` etc. This
breaks an assumption in existing regex (which expects a comma).
Support such device strings and add a couple of testcases to validate.
(cherry picked from commit db713bd0f5)
Co-authored-by: Anup Chenthamarakshan <anupcshan@users.noreply.github.com>
