Live Merge (snapshot deletion) fails with "has no backing file"

Issue

• A live merge failed with the following error reported in the vdsm log on the host on which the VM was running;

jsonrpc.Executor/2::ERROR::2016-05-09 14:30:03,799::vm::4882::virt.vm::(merge) vmId=`80c120af-2b21-4522-b21c-826d834a2587`::Live merge failed (job: 694e3d46-f29a-4640-b3f8-792b47308381)
Traceback (most recent call last):
  File "/usr/share/vdsm/virt/vm.py", line 4878, in merge
    flags)
  File "/usr/share/vdsm/virt/virdomain.py", line 68, in f
    ret = attr(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/libvirtconnection.py", line 124, in wrapper
    ret = f(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/utils.py", line 1313, in wrapper
    return func(inst, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 668, in blockCommit
    if ret == -1: raise libvirtError ('virDomainBlockCommit() failed', dom=self)
libvirtError: invalid argument: top '/rhev/data-center/00000002-0002-0002-0002-000000000225/6eb580c4-9421-4ecf-ae39-e7487bd83beb/images/fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/../fb1aa7e5-04e9-4b94-a02c-e27552efc19b/889b39f4-f028-4af3-b416-6cf742e97746' in chain for '/rhev/data-center/00000002-0002-0002-0002-000000000225/6eb580c4-9421-4ecf-ae39-e7487bd83beb/images/fb1aa7e5-04e9-4b94-a02c-e27552efc19b/3e081456-4f0c-4080-9c79-e731d43a6eaf' has no backing file