stat: fixing bw_agg reporting

It was wrongly set to the mean value instead of the agg one.
io_u: Using initialized local variable

ddir was feed with io_u->ddir at init time but didn't got used before
reassign it to the same value or another one.

That was making this init useless.

This patch simplify this portion of code by using the initialized
variable.
Merge branch 'erwan/clang' of https://github.com/enovance/fio
Fix propagation of error value on failure to connect to fio server

Fio does detect the error and exits, but it doesn't exit with
a non-zero exit value.

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