This commit addresses two similar (but distinct) bugs.

(1) 'ioping -c' was needlessly sleeping after the last iteration
(and before showing final stats). Fix it by moving the check
to before the usleep(), not after.

(2) 'ioping -w' was going over the time limit specified. For example,
'ioping -w 7 -i 2' was taking 8 seconds to run, not 7 or less.
Fix it by moving the check to before usleep(), and taking
the interval (ie usleep argument) into account.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>