Description of problem:

After a Live Storage Migration (LSM), a disk remains in "locked" status and the LSM sequence doesn't complete on the engine side. VmReplicateDiskFinishVDSCommand and DeleteImageGroupVDSCommand are never executed.

The associated job table entry in the RHEV database remains "STARTED".

 correlation_id |                job_id                |   action_type   |                     description                     | status  
----------------+--------------------------------------+-----------------+-----------------------------------------------------+---------
 edf0edf        | de4e97cf-e747-4657-bd07-e60aa278c0f1 | LiveMigrateDisk | Migrating Disk lsm-vm_Disk1 from LSM_GFW to NFS_GFW | STARTED

In the Admin Portal, the Disks menu will report the disk attached to the VM in "locked" status.

The engine sequence below completes but VmReplicateDiskFinishVDSCommand and DeleteImageGroupVDSCommand are never executed after the SyncImageGroupDataVDSCommand.

CloneImageGroupStructureVDSCommand
VmReplicateDiskStartVDSCommand
SyncImageGroupDataVDSCommand

I have been able to recreate this several times by live migrating 20 (arbitrary number) disks at once.

Version-Release number of selected component (if applicable):

Test environment;

   - RHEV-M 3.4.3 
   - Single host with (essentially) vdsm-4.14.13-2

How reproducible:

If I try to live migrate 20 disks at once I have encountered this problem every time. 

Steps to Reproduce:

1. In my specific case I created a pool of 20 VMs based off a template in an NFS data domain. 
2. I then started all 20 VMs. 
3. I then copied the template to a second NFS domain.
4. I then live migrated all 20 disks to the second NFS domain.

Actual results:

One of the 20 failed as described above.

Expected results:

All of the LSMs should complete and the associated jobs in the database be marked as "FINISHED".