MFV r336952: 9192 explicitly pass good_writes to vdev_uberblock/label_sync

MFV r336952: 9192 explicitly pass good_writes to vdev_uberblock/label_sync

Currently vdev_label_sync and vdev_uberblock_sync take a zio_t and assume
that its io_private is a pointer to the good_writes count. They should
instead accept this argument explicitly.

illumos/illumos-gate@a3b5583021b7b45676bf1f0cc68adf7a97900b56

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Author: Matthew Ahrens <mahrens@delphix.com>