ETA no longer works when -o specified

Regarding fio version fio-2.1.9-17-gd9b1 (after April 11, 2014):

A recent change (5e1d8745471d1f315113c5c3fd8b93809d9ddff9) caused stdout
to be closed when -o was specified, which prevents ETA output from showing
up on stdout even when, e.g., json is being saved in the file.

This patch continues to close f_out so that there is no leak if multiple -o
options are specified, but doesn't close stdout.  Hence, ETA works again
when it should.

Signed-off-by: Jens Axboe <axboe@fb.com>
Make rbd engine use aio flush

The fio's option "fsync" can make rbd engine issue sync request. In practice,
we would like to use aio_rbd_flush to make it non-block. So it will be more
reliable to use fio to evaluate actual io scene like qemu.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>