Fix ETA calculations

Fix ETA calculations

There are a couple of issues in eta.c:

- The comparison for time- vs. rate-based ETA calculation is done the
  wrong way round.
- The elapsed ramp time should only be subtracted when the thread has
  indeed entered the ramp phase.
- Currently jobs that are stonewalled are not taken into account for ETA
  calculation. This patch at least fixes this for the case that there is
  only a single job per stonewall group.
---

This patch tries to fix some issues I have found, this may
also be related to the ones mentioned earlier in
http://www.spinics.net/lists/fio/msg04187.html

The part regarding stonewalled jobs may require some further work, but
at least it gives proper values now for my standard fio runs containing
just a sequence of singular jobs.

Also, I'm still wondering about the intention behind the way done_secs
is meant to work. It cumulates time spent in finished jobs globally, but
is being used in per-job ETA calculations. This seems to break at
least for the case of stonewalled jobs, too.

Signed-off-by: Jens Axboe <axboe@fb.com>