ceph: re-send AIO write request when getting -EOLDSNAP error

When receiving -EOLDSNAP from OSD, we need to re-send corresponding
write request. Due to locking issue, we can send new request inside
another OSD request's complete callback. So we use worker to re-send
request for AIO write.

Signed-off-by: Yan, Zheng <zyan@redhat.com>