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>
Xyratex-bug-id: MRP-456
Signed-off-by: Bob Glossman <bogl@whamcloud.com>
Change-Id: I896519ed11abd301a889f658f96950ec15e76f97
Reviewed-on: http://review.whamcloud.com/3480
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <tappro@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>