LU-989 ldlm: Fix client's import destruction

LU-989 ldlm: Fix client's import destruction

Move client's import destruction from disconnect to cleanup phase
The patch allows to use connect after disconnect.

Xyratex-bug-id: MRP-288
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Signed-off-by: Bob Glossman <bogl@whamcloud.com>
Change-Id: I0a63f66205ac5931ead0acea492f3e480669e237
Reviewed-on: http://review.whamcloud.com/2664
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>