LU-4942 at: per-export lock callback timeout

LU-4942 at: per-export lock callback timeout

The lock callback timeout is calculated as an average per namespace.
This does not reflect individual client behavior.
Instead, we should calculate it on a per-export basis.

Signed-off-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Change-Id: I12e3fc5f8d261cce252fcf13f22193273dc054ee
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-by: Alexey Lyashkov <Alexey_Lyashkov@xyratex.com>
Xyratex-bug-id: MRP-417
Reviewed-on: http://review.whamcloud.com/9336
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>