Adds check for numberio during verify phase.

Adds check for numberio during verify phase.

Currently, fio checks the block offset number in a block's header during
the verify phase.
We add a check for the io number (numberio) to detect stale blocks. This
check is performed only on workloads that write data, as those workloads
know what numberio was written to each block.
td->io_issues[ddir] = 0; was removed so that numberio does not get reset
at each iteration; we want numberio to keep incrementing to reflect
how many times the same data was written.

Signed-off-by: Juan Casse <jcasse@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Fixed typo.
Signed-off-by: Jens Axboe <axboe@kernel.dk>