Illumos #2067: uninitialized variables in zfs(1M) may make snapshots undestroyable

Reviewed by: Joshua M. Clulow <josh@sysmgr.org>
Reviewed by: Milan Jurik <milan.jurik@xylab.cz>
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Steve Gonczi <gonczi@comcast.net>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
https://www.illumos.org/issues/2067

Ported by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>