OpenZFS 8898 - creating fs with checksum=skein on the boot pools fails ungracefully

OpenZFS 8898 - creating fs with checksum=skein on the boot pools fails ungracefully

Authored by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Toomas Soome <tsoome@me.com>
Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Approved by: Dan McDonald <danmcd@joyent.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
OpenZFS-issue: https://www.illumos.org/issues/8898
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/9fa2266d9a
Closes #7031