MRP-1455 ldlm: fixed soft lockup in target_handle_connect

There is no pair cfs_spin_unlock(&target->obd_recovery_task_lock)
when export is failed in target_handle_connect.
Bug is occurred when we have class_disconnect_stale_export
vs target_handle_connect race.

Change-Id: I482cf3c44dc8e1bc965d455ead9ae7b07ad51644
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/888
Tested-by: Jenkins
Reviewed-by: Andrew Perepechko <Andrew_Perepechko@xyratex.com>
Reviewed-by: Alexey Lyashkov <Alexey_Lyashkov@xyratex.com>
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>