OpenZFS 7736 - ZFS Performance tests should log FIO summary output

Authored by: Ahmed G <ahmedg@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Stephen Blinick <stephen.blinick@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

Porting Notes:

• Using $FIO until 7290 is ported.

OpenZFS-issue: https://www.illumos.org/issues/7736
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/7a61309
Closes #5827