Libaio engine support for iodepth_batch_complete=0

Libaio engine support for iodepth_batch_complete=0

Previously, even if iodepth_batch_complete=0, the libaio engine
passed in non-zero values for the min_nr value for io_getevents.
This patch makes min_nr always 0 if iodepth_batch_complete == 0,
and if multiple events are required at a higher level, then
we poll io_getevents multiple times for the events.

Signed-off-by: Dan Ehrenberg <dehrenberg@google.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>