OpenZFS 9184 - Add ZFS performance test for fixed blocksize random read/write IO

OpenZFS 9184 - Add ZFS performance test for fixed blocksize random read/write IO

This change introduces a new performance test which does random reads
and writes, but instead of using `bssplit` to determine the block size,
it uses a fixed blocksize. Additionally, some new IO sizes are added to
other tests and timestamp data is recorded with the performance data.

Authored by: Ahmed Gahnem <ahmedg@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Ported-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: John Wren Kennedy <john.kennedy@delphix.com>
Requires-builders: perf

OpenZFS-issue: https://www.illumos.org/issues/9184
OpenZFS-commit: https://github.com/openzfs/openzfs/pull/659
External-issue: DLPX-46724
Closes #7660