t/zbd: Fix test 2 and 3 result handling

t/zbd: Fix test 2 and 3 result handling

Removal of the message "No I/O performed" when fio does not execute any
I/O broke zbd tests 2 and 3 as this message is looked after to test for
success. Fix this by looking for a "Run status" line starting with
"WRITE:" for test 2 and "READ:" for test 3. The run status lines are not
printed when no I/O is performed. Testing for the absence of these
strings thus allows to easily test if I/Os where executed or not.

Fixes: ff3aa922570c ("Kill "No I/O performed by ..." message")
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>