Rescan enclosure sysfs path on import

When you create a pool, zfs writes vd->vdev_enc_sysfs_path with the
enclosure sysfs path to the fault LEDs, like:

    vdev_enc_sysfs_path = /sys/class/enclosure/0:0:1:0/SLOT8

However, this enclosure path doesn't get updated on successive imports
even if enclosure path to the disk changes. This patch fixes the issue.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #11950
Closes #12095