Description of problem:
When performing live snapshot on a VM the operation fails and leave the disks in locked state

Version-Release number of selected component (if applicable):
4.4

How reproducible:
100%

Steps to Reproduce:
1. Perform live snapshot

Additional info:

2020-04-01 16:46:06,134+0200 INFO  (virt/80f9f8fd) [virt.vm] (vmId='ddb201fb-dccc-4d9f-8b7f-08cc66e0fece') Taking a live snapshot (drives=vdb,memory=True) (snapsh
ot:350)
2020-04-01 16:46:06,379+0200 WARN  (qgapoller/2) [virt.periodic.VmDispatcher] could not run <function QemuGuestAgentPoller.start.<locals>.per_vm_operation.<locals
>.<lambda> at 0x7f0e801c58c8> on ['ddb201fb-dccc-4d9f-8b7f-08cc66e0fece'] (periodic:289)
2020-04-01 16:46:06,469+0200 ERROR (virt/80f9f8fd) [virt.vm] (vmId='ddb201fb-dccc-4d9f-8b7f-08cc66e0fece') Unable to take snapshot (snapshot:354)
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/vdsm/virt/jobs/snapshot.py", line 351, in snapshot
    self.vm.run_dom_snapshot(snapxml, snap_flags)
  File "/usr/lib/python3.6/site-packages/vdsm/virt/vm.py", line 5567, in run_dom_snapshot
    self._dom.snapshotCreateXML(snapxml, snap_flags)
  File "/usr/lib/python3.6/site-packages/vdsm/virt/virdomain.py", line 101, in f
    ret = attr(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/vdsm/common/libvirtconnection.py", line 131, in wrapper
    ret = f(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/vdsm/common/function.py", line 94, in wrapper
    return func(inst, *args, **kwargs)
  File "/usr/lib64/python3.6/site-packages/libvirt.py", line 2800, in snapshotCreateXML
    if ret is None:raise libvirtError('virDomainSnapshotCreateXML() failed', dom=self)
libvirt.libvirtError: internal error: unable to execute QEMU command 'blockdev-add': Image is not in qcow2 format