Add retry_request_cb in BlockDevOps to do device specific retry action.
Backend's timer would be registered only when the backend is set 'retry'
on errors and the device supports retry action.
Signed-off-by: Jiahui Cen <cenjiahui(a)huawei.com>
Signed-off-by: Ying Fang <fangying1(a)huawei.com>
