fio: reset more counters when ramp time has elapsed

fio: reset more counters when ramp time has elapsed

Currently,

fio --name=test --ramp_time=2 --time_based=1 --runtime=2s --size=1M

will produce an output line like

  IO depths    : 1=184.7%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%

184.7% appears because the denominator used in the IO depth calculation
is reset at the conclusion of ramp_time but the numerator is not.
Latency and other IO depth statistics also include data from IOs
completed during ramp time. This patch resets these counters when ramp
time is over.

Tested-by: Sebastien Boisvert <sboisvert@gydle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>