OpenZFS 8076 - zfs-tests suite fails rootpool_002_neg

OpenZFS 8076 - zfs-tests suite fails rootpool_002_neg

Authored by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: John Kennedy <jwk404@gmail.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: bunder2015 <omfgbunder@gmail.com>
OpenZFS-issue: https://www.illumos.org/issues/8076
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/ab3407e
Closes #6162