[PATCH] SG IO engine: reduce allocations and memory leaks

[PATCH] SG IO engine: reduce allocations and memory leaks

We currently do 3 allocations and frees in the queued getevents
handler, we can easily reduce that to 0 by statically allocating
the buffers at init time.

The cleanup handler didn't free any of the currently allocated
structures, fix that up.

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