Description of problem:

When I run preview of snapshot with memory in basic-suite-4.2 oVirt system test posted at https://gerrit.ovirt.org/#/c/86571/4, the VM fails to start with the following error:

  Traceback (most recent call last):
    File "/usr/lib/python2.7/site-packages/vdsm/API.py", line 225, in create
      return self._cif.createVm(vmParams)
    File "/usr/lib/python2.7/site-packages/vdsm/clientIF.py", line 558, in createVm
      vm = Vm(self, vmParams, vmRecover)
    File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 360, in __init__
      self._src_domain_xml, params['xml'])
    File "/usr/lib/python2.7/site-packages/vdsm/virt/vm.py", line 2937, in _correct_disk_volumes_from_xml
      change_disk(element, devices, self.log)
    File "/usr/lib/python2.7/site-packages/vdsm/virt/vmdevices/storagexml.py", line 260, in change_disk
      serial = vmxml.text(vmxml.find_first(disk_element, 'serial'))
    File "/usr/lib/python2.7/site-packages/vdsm/virt/vmxml.py", line 112, in find_first
      raise NotFound((element, tag,))
  NotFound: (<Element 'disk' at 0x7f64a418a990>, 'serial')

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

Current Vdsm from ovirt-4.2 branch.

How reproducible:

100%

Steps to Reproduce:

Run the OST from gerrit URL given above on basic-suite-4.2 with current Vdsm ovirt-4.2 branch.

Actual results:

The VM fails to start.

Expected results:

The VM starts from the given snapshot.