Add enumerated vdev names to 'zpool iostat -v' and 'zpool list -v'

This commit adds enumerated names to disambiguate between the
different vdevs. Previously only 'zpool status' showed enumerated
vdev names, now 'zpool list -v' and 'zpool iostat -v' also shows
the enumerated vdev names.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Dipak Ghosh <dipak.ghosh@hpe.com>
Signed-off-by: Akash B <akash-b@hpe.com>
Closes #12510
Closes #13031