Description of problem:
If restarting VDSM during live storage migration, there is a task in db (iveMigrateVmDisksParameters) that is not deleted:

engine=# select task_id, action_type, status, task_type, vdsm_task_id, action_params_class from async_tasks;
               task_id                | action_type | status | task_type |             vdsm_task_id             |                       action_params_class                        
--------------------------------------+-------------+--------+-----------+--------------------------------------+------------------------------------------------------------------
 b5658a22-dc22-40e1-8275-ab29289939e3 |        1011 |      2 |         3 | 7114d94d-8d33-442e-8fb8-c43a841d58d2 | org.ovirt.engine.core.common.action.LiveMigrateVmDisksParameters 
 9d6eee72-8b15-4b2d-bf45-e9e5691d728b |         211 |      2 |         5 | 00000000-0000-0000-0000-000000000000 | org.ovirt.engine.core.common.action.RemoveImageParameters        
(2 rows

In vdsm there is no running tasks:
[root@aqua-vds4 ~]# vdsClient -s 0 getAllTasks

[root@aqua-vds5 ~]# vdsClient -s 0 getAllTasks

This scenario cause that the Auto-generated snapshot is locked and the vms disk is locked as well and this is stayed that way until manual intervention. 

Version-Release number of selected component (if applicable):
vdsm-4.14.7-1.el6ev.x86_64
rhevm-3.4.0-0.20.el6ev.noarch

How reproducible:
100%

Steps to Reproduce:
1. LSM vm disk
2. restart vdsm during LSM
3.

Actual results:
Explained above

Expected results:
should fail gracefully 

Additional info: