Illumos #3006

3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first
     argument is zero

Reviewed by Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by George Wilson <george.wilson@delphix.com>
Approved by Eric Schrock <eric.schrock@delphix.com>

References:
  illumos/illumos-gate@fb09f5aad449c97fe309678f3f604982b563a96f
  https://illumos.org/issues/3006

Requires:
  zfsonlinux/spl@1c6d149feb4033e4a56fb987004edc5d45288bcb

Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1509