engines/rbd: add support for rbd_invalidate_cache()

Signed-off-by: Jens Axboe <axboe@fb.com>
engines/rbd: use rbd_aio_is_complete() and add TRIM support

Using fri->io_complete is potentially racy, since we have no
locking around checking and waiting. Use the API provided
function to check for completion instead.

Add support for TRIM through rbd_aio_discard().

Cleanup the queue interface and completion creation.

Signed-off-by: Jens Axboe <axboe@fb.com>
engines/rbd: remove unused rbd_options->td

Signed-off-by: Jens Axboe <axboe@fb.com>
engines/rbd: add option to busy poll on event completion

Signed-off-by: Jens Axboe <axboe@fb.com>
engines/glfs_async: add trim support

If available.

Signed-off-by: Jens Axboe <axboe@fb.com>
engines/glusterfs_async: cleanups

- Style issues
- Unnecessary casts
- Unnecessary variables inits

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