Sync AUX label during pool import

Spare and l2cache vdev labels are not updated during import. Therefore,
if disk paths are updated between pool export and import, the AUX label
still shows the old paths. This patch syncs the AUX label
during import to show the correct path information.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Umer Saleem <usaleem@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #15817