LU-1749 llog: MDT should work if cancel llog failed (-ESTALE)

LU-1749 llog: MDT should work if cancel llog failed (-ESTALE)

Cancel catlog may be stale, in this case MDT should continue to work.

port of b2_3 patch e5d5cd20169b476cdb4fe4857d64aef4bf03d497

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: I85d571a953b2a34d51d586595e271933a016b04f
Reviewed-on: http://review.whamcloud.com/4742
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>