Illumos #5244 zio pipeline callers should explicitly invoke next stage

References:
https://www.illumos.org/projects/illumos-gate//issues/5244
https://reviews.csiden.org/r/119/diff/#

Porting Notes:
1. The unported "2932 support crash dumps to raidz, etc. pools" caused a
merge conflict due to a copyright difference in module/zfs/vdev_raidz.c.
2. The unported "4128 disks in zpools never go away when pulled" and
additional Linux-specific changes caused merge conflicts in
module/zfs/vdev_disk.c.
3. Our changes to use the TQ_PUSHPAGE extension and vdev_file_taskq
caused merge conflicts in module/zfs/vdev_file.c. The taskq import that
I plan to send in the future would have prevented this particular
conflict.

Reviewed by: Matthew Ahrens mahrens@delphix.com
Reviewed by: Adam Leventhal ahl@delphix.com
Reviewed by: Alex Reece alex.reece@delphix.com
Reviewed by: Christopher Siden christopher.siden@delphix.com
Ported-by: Richard Yao <richard.yao@clusterhq.com>