OpenZFS 9164 - assert: newds == os->os_dsl_dataset

OpenZFS 9164 - assert: newds == os->os_dsl_dataset

Authored by: Andriy Gapon <avg@FreeBSD.org>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Don Brady <don.brady@delphix.com>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Richard Lowe <richlowe@richlowe.net>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Porting Notes:
* Re-enabled and tweaked the zpool_upgrade_007_pos test case
  to successfully run in under 5 minutes.

OpenZFS-issue: https://www.illumos.org/issues/9164
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/0e776dc06a
Closes #6112
Closes #7336