LU-1194 llog: fix for not sync llcd at thread stop

LU-1194 llog: fix for not sync llcd at thread stop

If llog_obd_repl_cancel() happend between llog_sync() and
class_import_put() at filter_llog_finish(), llog_recov_thread_stop()
throw LBUG. This patch fix this issue by adding new flags to llog_ctxt.

Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Reviewed-by: Andriy Skulysh <andriy_skulysh@xyratex.com>
Reviewed-by: Alexander Zarochentsev <alexander_zarochentsev@xyratex.com>
Xyratex-bug-id: MRP-456
Change-Id: Ife79adfe6cde0f2090776cd27cd87f65c1e988e2
Reviewed-on: http://review.whamcloud.com/2789
Reviewed-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <tappro@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>