LU-2701 osp: wake up sync thread

LU-2701 osp: wake up sync thread

osp_sync_process_committed() to wake up sync thread when it
is requested to stop (e.g. umount) and there is no pending
work left. the patch adds a sanity check to ensure this
process is not taking too long.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I5251013afc2aee55627c806a11eb826a9d3dbec9
Reviewed-on: http://review.whamcloud.com/5463
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>